Patent Publication Number: US-8533330-B2

Title: Relay server and relay communication system arranged to share resources between networks

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. 119 to Japanese Patent Application No. 2006-333500, filed on Dec. 11, 2006, No. 2006-335539, filed on Dec. 13, 2006, and No. 2006-341335, filed on Dec. 19, 2006, which applications are hereby incorporated by reference in their entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a relay communication system which can enable communications with a terminal in a different local area network (LAN) over a wide area network (WAN) and a relay server used in the system, and more particularly, to a technology of allowing a terminal in a LAN to operate resources retained by a terminal in a different LAN. 
     2. Description of the Related Art 
     A communication technology called a virtual private network (VPN) is known. By using this communication technology, it is possible to use a remote LAN like a directly connected network. For example, terminals connected to LANs of plural branches provided in local areas, respectively, can communicate with each other over the Internet. 
     Various systems for such a type of technology have been suggested (for example, see Japanese Unexamined Patent Publication No. 2002-217938). 
     BRIEF SUMMARY OF THE INVENTION 
     However, such a type of system tends to be stiff because a network is virtually constructed. Accordingly, it is not easy to construct an expansible and flexible system and the suggested systems have both merits and demerits in function, cost, and the like. 
     For example, since resources in a LAN are managed under the same protocol and the system configuration is not much complicated, plural terminals can easily share the resources. However, when a communication system includes plural LANs over a WAN, it is not possible to easily cope with such intention that resources such as folders are shared with plural terminals or files or that a file retained by a terminal is deleted by a different terminal. This is also true in a case where different protocols are used in the LANs. 
     The resources retained by the terminals vary endlessly due to deletion or movement thereof, but it is not easy to dynamically cope with such a variation. 
     Access statuses of specific relay points or terminals constructing a system also vary endlessly due to ON/OFF of a power source or log ON/OFF. The system may be downed for some reasons. It is not also easy to dynamically cope with the variation in access status. 
     A terminal registered in a LAN may move to another LAN. In this case, the access setting varies in a movement source and a movement destination and it is thus necessary to sequentially update the management setting of a resource managed by the terminal with the variation. 
     There is a need for a flexible communication system which can select a resource handling method depending on the situations. 
     An object of the invention is to provide a relay communication system which can be easily operated and which can allow terminals to share and operate a resource with a necessary opposite terminal even when the terminals are connected to different LANs and managed under different protocols. Another object of the invention is to provide a relay server used for the system. Still another object of the invention is to provide a dynamic relay communication system which has excellent expansibility and flexibility and which can cope with a variation of resources or a variation in access status of relay points due to movement or the like of the resources. 
     Still another object of the invention is to provide a relay server suitable for a dynamic relay communication system and which can be used without any consciousness, since it does not require troublesome works such as a change of set conditions even when a terminal having been registered move between LANs. 
     Still another object of the invention is to provide a relay server which can allow a user to select a resource handling method. 
     According to a first aspect of the invention for accomplishing the above-mentioned object, there is provided a relay server which is connected to a LAN and which can communicate with a relay server in a different LAN, the relay server including: an account information registering unit that stores information on client terminals connected to the LAN; a relay group information registering unit that stores relay group information including information on a group of relay servers permitting accesses to each other; a shared resource information registering unit that stores shared resource information including information on resources, state information indicating statuses of the resources, and information on the client terminals sharing the resources; a check unit that checks whether the client terminals stored in the account information registering unit can be accessed; a relay group information notifying unit that updates the relay group information and transmits a change notification of the relay group information to the relevant relay server, when checking that a client terminal is changed in access status; and a shared resource information notifying unit that updates the relevant shared resource information and transmits a change notification of the shared resource information to the relevant client terminal which is stored in the account information registering unit, when receiving the change notification of the relay group information. 
     According to a second aspect of the invention, there is provided a relay server which is connected to a LAN and which can communicate with a relay server in a different LAN, the relay server including: an account information registering unit that stores information on client terminals connected to the LAN; a relay group information registering unit that stores relay group information including information on a group of relay servers permitting accesses to each other and status information indicating statuses of the relay servers; a shared resource information registering unit that stores shared resource information including information on resources, status information indicating statuses of the resources, and information on the client terminals sharing the resources; a check unit that checks whether the relay servers stored in the relay group information registering unit can be accessed; a relay group information notifying unit that updates the relay group information and transmits a change notification of the relay group information to the relevant relay server, when checking that a relay server is changed in access status; and a shared resource information notifying unit that updates the relevant shared resource information and transmits a change notification of the shared resource information to the relevant client terminal which is stored in the account information registering unit, when receiving the change notification of the relay group information. 
     According to a third aspect of the invention, there is provided a relay communication system including: a plurality of LANs; and a relay server and client terminals connected to each LAN. Here, the relay server includes: an account information registering unit that stores information on client terminals connected to the LAN; a relay group information registering unit that stores relay group information including information on a group of relay servers permitting accesses to each other; a shared resource information registering unit that stores shared resource information including information on resources, state information indicating statuses of the resources, and information on the client terminals sharing the resources; a check unit that checks whether the client terminals stored in the account information registering unit can be accessed; a relay group information notifying unit that updates the relay group information and transmits a change notification of the relay group information to the relevant relay server, when checking that a client terminal is changed in access status; and a shared resource information notifying unit that updates the relevant shared resource information and transmits a change notification of the shared resource information to the client terminals connected to the same LAN, when receiving the change notification of the relay group information. The relay group information and the shared resource information held in the relay communication system are automatically updated. 
     According to a fourth of the invention, there is provided a relay communication system including: a plurality of LANs; and a relay server and client terminals connected to each LAN. Here, the relay server includes: an account information registering unit that stores information on client terminals connected to the LAN; a relay group information registering unit that stores relay group information including information on a group of relay servers permitting accesses to each other and status information indicating statuses of the relay servers; a shared resource information registering unit that stores shared resource information including information on resources, status information indicating statuses of the resources, and information on the client terminals sharing the resources; a check unit that checks whether the relay servers stored in the relay group information registering unit can be accessed; a relay group information notifying unit that updates the relay group information and transmits a change notification of the relay group information to the relevant relay server, when checking that a relay server is changed in access status; and a shared resource information notifying unit that updates the relevant shared resource information and transmits a change notification of the shared resource information to the relevant client terminal which is stored in the account information registering unit, when receiving the change notification of the relay group information. The relay group information and the shared resource information held in the relay communication system are automatically updated. 
     According to a fifth aspect of the invention, there is provided a relay server which is connected to a LAN and which can communicate with a relay server in a different LAN, the relay server including: an account information registering unit that stores information on client terminals connected to the LAN; and a relay group information registering unit that stores relay group information including information on a group of relay servers permitting accesses to each other and information on the client terminals registered in the respective relay servers. Here, when an access request is received from a client terminal stored in the account information registering unit of the different relay server, the relay server in which the client terminal having transmitted the access request is registered is specified on the basis of the relay group information and it is determined whether the access should be permitted by inquiring of the specified relay server. 
     A sixth aspect of the invention provides the relay server according to the fifth aspect of the invention, wherein the relay group information includes access information which is created every client terminal and which indicates the relay server as an access destination of the corresponding client terminal, and wherein when the access request is received from the client terminal stored in the account information registering unit, details of the access information of the client terminal included in the relay group information stored in the relay server is updated and a change notification of the relay group information is transmitted to the corresponding different relay server. 
     A seventh aspect of the invention provides the relay server according to the sixth aspect of the invention, wherein when the access of the client terminal stored in the account information registering unit of the different relay server is permitted, details of the access information of the client terminal included in the relay group information stored in the relay server is updated and a change notification of the relay group information is transmitted to the corresponding different relay server. 
     According to a eighth aspect of the invention, there is provided a relay server which is connected to a LAN and which can communicate with a relay server in a different LAN, the relay server including: an account information registering unit that stores information on client terminals connected to the LAN; a relay group information registering unit that stores relay group information including information on a group of relay servers permitting accesses to each other; a shared resource information registering unit that stores shared resource information including information on resources and information on the client terminals sharing the resources; and 
     a relay unit that relays a resource operation on the basis of the relay group information and the shared resource information, when receiving a command for operating a resource, which can be operated by the client terminal connected to the different LAN, from the client terminal stored in the account information registering unit, wherein the resource operation includes a synchronous mode in which a seeming operation based on a change of the shared resource information and an essential operation of a resource are synchronized with each other and an asynchronous mode in which the seeming operation based on a change of the shared resource information and the essential operation of a resource are not synchronized with each other. 
     A ninth aspect of the invention provides the relay server according to the eighth aspect of the invention, wherein when the operation command for operating a resource which can be operated by the client terminal connected to the different LAN is received in the synchronous mode, the client terminal which can operate the resource is specified on the basis of the shared resource information, the relay server in which the specified client terminal is registered is specified on the basis of the relay group information, and the operation command is transmitted to the client terminal which can operate the resource through the specified relay server. 
     A tenth aspect of the invention provides the relay server according to the eighth or ninth aspect of the invention, wherein when the operation command for operating a resource which can be operated by the client terminal connected to the different LAN is received in the synchronous mode and the seeming operation can be performed by changing the shared resource information, the shared resource information is updated, and wherein when the seeming operation cannot be performed by changing the shared resource information, the client terminal which can operate the resource is specified on the basis of the shared resource information, the relay server in which the specified client terminal is registered is specified on the basis of the relay group information, and the operation command is transmitted to the client terminal which can operate the resource. 
     An eleventh aspect of the invention provides the relay server according to any one of the eighth to tenth aspect of the invention, wherein a mode is set in advance. 
     A twelfth aspect of the invention provides the relay server according to any one of the eighth to tenth aspect of the invention, wherein a mode can be selected at the time of operating a resource. 
     According to a thirteenth aspect of the invention, there is provided a management method using a relay server which is connected to a LAN and which can communicate with a relay server in a different LAN, the management method including: storing information on client terminals connected to the LAN; storing relay group information including information on a group of relay servers permitting accesses to each other; storing shared resource information including information on resources, state information indicating statuses of the resources, and information on the client terminals sharing the resources; checking whether the client terminals stored in the registering of the account information can be accessed; updating the relay group information and transmitting a change notification of the relay group information to the relevant relay server, when checking that a client terminal is changed in access status; and updating the relevant shared resource information and transmitting a change notification of the shared resource information to the relevant client terminal stored in the registering of the account information, when receiving the change notification of the relay group information. 
     According to a fourteenth aspect of the invention, there is provided a management method using a relay server which is connected to a LAN and which can communicate with a relay server in a different LAN, the management method including: storing information on client terminals connected to the LAN; storing relay group information including information on a group of relay servers permitting accesses to each other and status information indicating statuses of the relay servers; storing shared resource information including information on resources, status information indicating statuses of the resources, and information on the client terminals sharing the resources; checking whether the relay servers stored in the registering of the relay group information can be accessed; updating the relay group information and transmitting a change notification of the relay group information to the relevant relay server, when detecting a relay server changed in access status; and updating the relevant shared resource information and transmitting a change notification of the shared resource information to the relevant client terminal which is stored in the registering of the account information, when receiving the change notification of the relay group information. 
     According to a fifteenth aspect of the invention, there is provided a management method of a relay communication system which has a plurality of LANs and a relay server and client terminals connected to each LAN, the management method including: storing information on client terminals connected to the LAN; storing relay group information including information on a group of relay servers permitting accesses to each other; storing shared resource information including information on resources, state information indicating statuses of the resources, and information on the client terminals sharing the resources; checking whether the client terminals stored in the registering of the account information can be accessed; updating the relay group information and transmitting a change notification of the relay group information to the relevant relay server, when detecting a client terminal changed in access status; and updating the relevant shared resource information and transmitting a change notification of the shared resource information to the client terminals connected to the same LAN, when receiving the change notification of the relay group information, and wherein the relay group information and the shared resource information held in the relay communication system are automatically updated. 
     According to a sixteenth aspect of the invention, there is provided a management method of a relay communication system which has a plurality of LANs and a relay server and client terminals connected to each LAN, the management method including: storing information on client terminals connected to the LAN; storing relay group information including information on a group of relay servers permitting accesses to each other and status information indicating statuses of the relay servers; storing shared resource information including information on resources, status information indicating statuses of the resources, and information on the client terminals sharing the resources; checking whether the relay servers stored in the registering of the relay group information can be accessed; updating the relay group information and transmitting a change notification of the relay group information to the relevant relay server, when detecting a relay server changed in access status; and updating the relevant shared resource information and transmitting a change notification of the shared resource information to the relevant client terminal which is stored in the account information registering unit, when receiving the change notification of the relay group information, and wherein the relay group information and the shared resource information held in the relay communication system are automatically updated. 
     According to a seventeenth aspect of the invention, there is provided a management method using a relay server which is connected to a LAN and which can communicate with a relay server in a different LAN, the management method including: storing information on client terminals connected to the LAN; and storing relay group information including information on a group of relay servers permitting accesses to each other and information on the client terminals registered in the respective relay servers, wherein when an access request is received from a client terminal stored in the registering of the account information of the different relay server, the relay server in which the client terminal having transmitted the access request is registered is specified on the basis of the relay group information and it is determined whether the access should be permitted by inquiring of the specified relay server. 
     An eighteenth aspect of the invention provides the management method according to the seventeenth aspect of the invention, wherein the relay group information includes access information which is created every client terminal and which indicates the relay server as an access destination of the corresponding client terminal, and wherein when the access request is received from the client terminal stored in the registering of the account information, details of the access information of the client terminal included in the relay group information stored in the relay server is updated and a change notification of the relay group information is transmitted to the corresponding different relay server. 
     A nineteenth aspect of the invention provides the management method according to the eighteenth aspect of the invention, wherein when the access of the client terminal stored in the registering of the account information of the different relay server is permitted, details of the access information of the client terminal included in the relay group information stored in the relay server is updated and a change notification of the relay group information is transmitted to the corresponding different relay server. 
     According to a twentieth aspect of the invention, there is provided a management method using a relay server which is connected to a LAN and which can communicate with a relay server in a different LAN, the management method including: storing information on client terminals connected to the LAN; storing relay group information including information on a group of relay servers permitting accesses to each other; storing shared resource information including information on resources and information on the client terminals sharing the resources; and relaying a resource operation on the basis of the relay group information and the shared resource information, when receiving a command for operating a resource, which can be operated by the client terminal connected to the different LAN, from the client terminal stored in the registering of the account information, wherein the resource operation includes a synchronous mode in which a seeming operation based on a change of the shared resource information and an essential operation of a resource are synchronized with each other and an asynchronous mode in which the seeming operation based on a change of the shared resource information and the essential operation of a resource are not synchronized with each other. 
     A twenty-first aspect of the invention provides the management method according to the twentieth aspect of the invention, wherein when the operation command for operating a resource which can be operated by the client terminal connected to the different LAN is received in the synchronous mode, the client terminal which can operate the resource is specified on the basis of the shared resource information, the relay server in which the specified client terminal is registered is specified on the basis of the relay group information, and the operation command is transmitted to the client terminal which can operate the resource through the specified relay server. 
     A twenty-second aspect of the invention provides the management method according to the twentieth or twenty-first aspect of the invention, wherein when the operation command for operating a resource which can be operated by the client terminal connected to the different LAN is received in the synchronous mode and the seeming operation can be performed by changing the shared resource information, the shared resource information is updated, and wherein when the seeming operation cannot be performed by changing the shared resource information, the client terminal which can operate the resource is specified on the basis of the shared resource information, the relay server in which the specified client terminal is registered is specified on the basis of the relay group information, and the operation command is transmitted to the client terminal which can operate the resource. 
     Aspect twenty-third aspect of the invention provides the management method according to any one of the twentieth to twenty-second aspect of the invention, wherein a mode is set in advance. 
     Aspect twenty-fourth aspect of the invention provides the management method according to any one of the twentieth to twenty-second aspect of the invention, wherein a mode can be selected at the time of operating a resource. 
     In the relay communication system employing the relay server according to the invention, the client terminal in a different LAN can operate a resource held by a different client terminal over the WAN, as if the client terminal holds the resource. 
     The operating conditions of the relay servers and the client terminals are periodically monitored and checked and the relevant information is always updated. Accordingly, even when a change due to the deletion of a resource, a change in access status due to a power ON/OFF state or a log ON/OFF state of the relay servers or the client terminals, or an unexpected trouble occurs, the states can be easily grasped, thereby not causing a user&#39;s confusion. 
     It is possible to use the resources without any consciousness, since it does not require troublesome works such as a change of set conditions even when a terminal having been registered in a LAN moves to a different LAN. 
     One mode of both the synchronous mode in which the seeming operation and the essential operation of the resource are synchronized with each other and the asynchronous mode in which they are not synchronized with each other can be selected at the time of operating the resource, depending on it. For example, when the synchronous mode is selected in which the operation details accompany the status of the resource, the client terminal T having copied a file can operate the file directly after the copy operation. As a result, it is not necessary to indirectly operate the file through a relay communication and thus it is possible to reduce a communication process load thereafter. On the other hand, when the asynchronous mode is selected, it is possible to prevent the resource from being repeatedly created and thus to efficiently use the storage unit in the relay communication system. 
     Other features, elements, processes, steps, characteristics, and advantages of the invention will become more apparent from the following detailed description of preferred embodiments of the invention with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a network configuration of a relay communication system according to a first embodiment of the invention; 
         FIG. 2  is a functional block diagram illustrating an external server according to the first embodiment of the invention; 
         FIG. 3  is a functional block diagram illustrating a client terminal according to the first embodiment of the invention; 
         FIG. 4  is a functional block diagram illustrating a relay server according to the first embodiment of the invention; 
         FIG. 5  is a diagram illustrating a relation between the client terminal and the relay server and a relation between the relay server and the external server according to the first embodiment of the invention; 
         FIG. 6  is a diagram illustrating details of relay group information according to the first embodiment of the invention; 
         FIG. 7  is a diagram illustrating details of shared resource information according to the first embodiment of the invention; 
         FIG. 8  is a sequence diagram illustrating a communication process according to the first embodiment of the invention; 
         FIG. 9  is a sequence diagram of the communication process subsequent to  FIG. 8 ; 
         FIG. 10  is a diagram illustrating details of relay group information in a certain process according to the first embodiment of the invention; 
         FIG. 11  is a sequence diagram illustrating a communication process according to the first embodiment of the invention; 
         FIG. 12  is a diagram illustrating details of shared resource information in a certain process according to the first embodiment of the invention; 
         FIG. 13  is a diagram illustrating details of shared resource information in a certain process according to the first embodiment of the invention; 
         FIG. 14  is a diagram illustrating details of shared resource information in a certain process according to the first embodiment of the invention; 
         FIG. 15  is a sequence diagram of the communication process subsequent to  FIG. 11 ; 
         FIG. 16  is a diagram illustrating details of shared resource information in a certain process according to the first embodiment of the invention; 
         FIG. 17  is a diagram illustrating details of shared resource information in a certain process according to the first embodiment of the invention; 
         FIG. 18  is a sequence diagram illustrating a communication process according to the first embodiment of the invention; 
         FIG. 19  is a diagram illustrating details of shared resource information in a certain process according to the first embodiment of the invention; 
         FIG. 20  is a flowchart illustrating a process of a relay server according to a second embodiment of the invention; 
         FIG. 21  is a sequence diagram illustrating a communication process according to the second embodiment of the invention; 
         FIG. 22  is a diagram illustrating details of relay group information in a certain process according to the second embodiment of the invention; 
         FIG. 23  is a diagram illustrating details of shared resource information in a certain process according to the second embodiment of the invention; 
         FIG. 24  is a diagram illustrating details of relay group information in a certain process according to the second embodiment of the invention; 
         FIG. 25  is a diagram illustrating details of shared resource information in a certain process according to the second embodiment of the invention; 
         FIG. 26  is a diagram illustrating details of relay group information in a certain process according to the second embodiment of the invention; 
         FIG. 27  is a diagram illustrating details of shared resource information in a certain process according to the second embodiment of the invention; 
         FIG. 28  is a sequence diagram illustrating a communication process according to a third embodiment of the invention; 
         FIG. 29  is a sequence diagram illustrating a communication process according to the third embodiment of the invention; 
         FIG. 30  is a diagram illustrating details of relay group information in a certain process according to the third embodiment of the invention; 
         FIG. 31  is a diagram illustrating details of shared resource information in a certain process according to the third embodiment of the invention; 
         FIG. 32  is a diagram illustrating details of relay group information in a certain process according to the third embodiment of the invention; 
         FIG. 33  is a diagram illustrating details of shared resource information in a certain process according to the third embodiment of the invention; 
         FIG. 34  is a diagram illustrating details of relay group information in a certain process according to the third embodiment of the invention; 
         FIG. 35  is a diagram illustrating details of shared resource information in a certain process according to the third embodiment of the invention; 
         FIG. 36  is a diagram illustrating details of shared resource information according to a fourth embodiment of the invention; 
         FIG. 37  is a diagram illustrating details of shared resource information displayed by a communication device according to the fourth embodiment of the invention; 
         FIG. 38  is a sequence diagram illustrating a flow of a communication process in operating a resource according to the fourth embodiment of the invention; 
         FIG. 39  is a sequence diagram illustrating a flow of a communication process in operating a resource according to the fourth embodiment of the invention; 
         FIG. 40  is a sequence diagram illustrating a flow of a communication process in operating a resource according to the fourth embodiment of the invention; 
         FIG. 41  is a diagram illustrating details of shared resource information in a certain process according to the fourth embodiment of the invention; 
         FIG. 42  is a diagram illustrating details of shared resource information displayed by a communication device according to the fourth embodiment of the invention; 
         FIG. 43  is a diagram illustrating details of shared resource information in a certain process according to the fourth embodiment of the invention; and 
         FIG. 44  is a diagram illustrating details of shared resource information in a certain process according to the fourth embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Hereinafter, exemplary embodiments of the invention will be described with reference to the drawings. First, a basic configuration of a relay communication system according to a first embodiment the invention will be described. Then, concrete configurations of relay communication systems according to second, third, and fourth embodiments of the invention will be described in detail. 
     First Embodiment 
       FIG. 1  illustrates an entire configuration of a relay communication system according to the invention. As shown in  FIG. 1 , the relay communication system includes a plurality of LANs connected to a WAN. The relay communication system includes an external server S, relay servers R, client terminals T, and file servers F. Although an example using the external server S will be exemplified, the relay servers R may directly communicate with each other without using the external server S. 
     In this embodiment, a system using a session initiation protocol (SIP) as a communication protocol between the external server S and the relay servers R in the WAN and between the relay server R and the client terminals T in the respective LANs is exemplified. However, protocols other than the SIP may be used as a communication protocol between the servers and the terminals. 
     The WAN (Wide Area Network) is a network for connecting different LANs. In this embodiment, the Internet is exemplified as the WAN, but the invention is not limited to the Internet, but other networks similar thereto may be used. 
     A LAN (Local Area Network) is a relatively small-scale network which is constructed in a defined place. Plural LANs are provided and are constructed in places physically apart from each other. For example, in this embodiment, a LAN 1  is constructed in a branch A in Tokyo and LAN 2 , LAN 3 , and LAN 4  are constructed in branches B, C, and D of Osaka, Nagoya, and Fukuoka, respectively. Four LANs of the LAN 1 , LAN 2 , LAN 3 , and LAN 4  are connected to the Internet which is a global network. The number of LANs is not limited to four, but may be any other plural number. 
     External Server 
     The external server S is a device used in communications between the relay servers R disposed in the LANs and is disposed over the Internet. The external server S has a function of an SIP server. Specifically, the external server S has a function of an SIP proxy server for relaying SIP methods and responses and a function of an SIP registrar server for registering accounts of the relay servers R. The number of external servers S is not limited to one, but may be a plural number to function in a distributed manner. When a protocol other than the SIP is used, communications between the relay servers R can be directly controlled on the basis of the protocol and it is thus not necessary to provide the external server S serving as the SIP server. 
     A functional block diagram of the external server S is shown in  FIG. 2 . As shown in  FIG. 2 , the external server S includes a WAN interface  201 , a controller  202 , and a relay server account information database (DB)  203 . 
     The WAN interface  201  is an interface serving to communicate with devices such as the relay servers R connected to the Internet by the use of global IP addresses. 
     The relay server account information DB  203  is a database managing an account of the relay server R having requested for registration to be correlated with a global IP address. 
     The controller  202  is a processing unit serving to control various communications through the WAN interface  201  and controls a communication process in accordance with protocols such as a TCP/IP, a UDP, and an SIP. For example, the controller  202  serves to receive accounts of the relay servers R transmitted from the relay servers R and to register the received accounts in the relay server account information DB  203 . Alternatively, the controller  202  performs a process of relaying communication data such as various SIP methods and responses transmitted from a relay server R to another relay server R. The functions of the controller  202  and the like of the external server S will be described later. 
     Client Terminal 
     A client terminal T is a terminal which can be operated directly by a user. For example, a personal computer (PC) and the like used in a user&#39;s usual works corresponds to the client terminal T. Accordingly, plural client terminals T are generally disposed in a LAN. In this embodiment, an example is described in which client terminals  1 A and  1 B are connected to the LAN 1 , client terminals  2 A and  2 B are connected to the LAN 2 , client terminals  3 A and  3 B are connected to the LAN 3 , and client terminals  4 A and  4 B are connected to the LAN 4 . Private IP addresses which are uniquely managed only in the same LAN are given to the client terminals T. 
     A functional block diagram of the client terminal T is shown in  FIG. 3 . As shown in  FIG. 3 , the client terminal T includes a LAN interface  601 , a controller  602 , a resource storing unit  603 , a shared resource information database (DB)  604 , and a display unit  605 . 
     The LAN interface  601  is an interface for communicating with devices such as the relay server R or the file server F connected to the same LAN by the use of the private IP address. 
     The resource storing unit  603  stores essences of resources such as files or folders which can be operated by the client terminal T. 
     The shared resource information database (DB)  604  stores shared resource information  120  which includes information on resources held by the client terminals T and information on accounts of the client terminals T sharing the resources and in which information on shared resources held by the client terminals T is described. 
     The display unit  605  visually displays details of relay group information  100  to be described later or the shared resource information  120 . 
     The controller  602  is a processing unit for controlling various communications performed through the LAN interface  601 . The controller  602  serves to control communication processes in accordance with the protocols such as TCP/IP, UDP, and SIP. For example, the controller  602  performs processes of controlling movement, change, and deletion of the resources stored in the resource storing unit  603 . Alternatively, the controller  602  receives a change notification of the shared resource information  120  from the relay servers R and performs a process of updating the shared resource information  120  stored in the shared resource information DB  604 . The functions of the client terminal T including the controller  602  will be described later. 
     Relay Server 
     One relay server R is disposed in each LAN. Specifically, a relay server R 1  is disposed in LAN 1 , a relay server R 2  is disposed in LAN 2 , a relay server R 3  is disposed in LAN 3 , and a relay server R 4  is disposed in LAN 4 . 
     The relay server R is connected to the Internet as well as a LAN. The relay server R can communicate with the client terminals T connected to the same LAN and can communicate with the relay server R connected to a different LAN through the external server S. Accordingly, global IP addresses in addition to the private IP addresses are given to the relay servers R, respectively. 
     A functional block diagram of each relay server R is shown in  FIG. 4 . As shown in  FIG. 4 , the relay server R includes a LAN interface  501 , a WAN interface  502 , a controller  503 , an account information database (DB)  504 , a relay group information database (DB)  505 , and a shared resource information database (DB)  506 . 
     The LAN interface  501  is an interface that communicates with a client terminal T connected to a LAN by the use of the private IP address. For example, in LAN 1 , the relay server R 1  communicates with the client terminals  1 A and  1 B through the LAN interface  501 . 
     The WAN interface  502  is an interface that communicates with devices such as the external server S connected to the Internet  1  by the use of the global IP address. Although it is described in this embodiment that the relay server R includes the WAN interface  502 , a router may perform a connection to the Internet and the relay server R may be disposed under the control of the router. 
     Since the communications between the relay servers R and the client terminals T are performed using the SIP, the relay servers R have a function of an SIP registrar server. For example, the relay server R 2  connected to the LAN 2  serves as an SIP registrar server for registering accounts of the client terminals  2 A and  2 B connected to the LAN 2  in the account information DB  504  using the SIP. 
     Accordingly, as shown in  FIG. 5 , the relay server R serves as a server for receiving and registering the accounts from the client terminals T, in a relation with the client terminals T. In a relation with the external server S, the relay server serves as a client for transmitting and registering the accounts to the external server S. 
     The account information DB  504  is a database for managing the accounts of the client terminals T having requested for registration so as to be correlated with the private IP addresses. 
     The relay group information DB  505  is a database for managing the relay group information associated with the client terminals T registered in the account information DB. 
     The shared resource information DB  506  is a database for managing the shared resource information associated with the client terminals registered in the account information DB. 
     The controller  503  is a processing unit for controlling various communications performed through the LAN interface  501  and the WAN interface  502  and serves to control various communication processes in accordance with the protocols such as the TCP/IP, the UDP, and the SIP. For example, the controller  503  performs a process of transmitting its account to the external server S and requesting for registration of the account and a process of registering the accounts transmitted from the client terminals T connected to the same LAN in the account information DB  504 . Alternatively, the controller  503  performs a process of creating the relay group information  100  and storing the created relay group information in the relay group information DB  505  and a process of creating the shared resource information  120  and storing the created shared resource information in the shared resource information DB  506 . The functions of the relay servers R including the controller  503  will be described later. 
     File Server 
     The file server F is a server that is connected to a LAN to communicate with the client terminals T connected to the same LAN and can store essences of resources such as files or folders. That is, the file server F serves as resource storing unit substituted for the resource storing unit  603  of the client terminals T. That is, in this embodiment, the resources that can be operated by the client terminals T may be stored in a local disc of the corresponding terminal T or may be stored in the file server F as a network drive. Accordingly, as the file server F is shown in some LANs of the LAN 1  and LAN 3  in  FIG. 1 , the file server is not essential to the LAN but may be provided properly as needed. 
     The relay group information  100  and the shared resource information  120  which are information used in the relay communication system will be described now. 
     Relay Group Information 
     Details of the relay group information  100  are shown in  FIG. 6  and the like.  FIG. 6  illustrates the relay group information  100  which is exchanged between three relay servers R 1 , R 2 , and R 3  using the relay server R 1  as a start point and which is stored in the relay group information DBs  505 . The relay group information  100  includes a piece of group identification information  101  and information (relay account information)  102  on three relay servers R 1 , R 2 , and R 3  permitting connections to each other. 
     The group identification information  101  is information for identifying the relay group information  100 . A unique ID is given to each piece of relay group information every time of creation thereof and thus the relay group information is identified at a view. Accordingly, an operator or the like can specify a relay group by the use of the group identification information  101  and can easily change a group configuration. 
     The relay account information  102  includes information on the accounts of the relay servers R and the accounts of the client terminals T connected to the same LAN as a relay server R and registered in the relay server R. Specific names are given to the accounts of the relay servers R and the relay servers can be easily identified by a user. Similarly, specific names are given to the accounts of the client terminals T. For example, regarding the relay account information  102   a  of the relay server R 1  (rely-server1), a name  104  (branch A) is given to the account (relay-server1@net) of the relay server R 1 . Names (for example, terminal  1 A) are given to the accounts (for example, user1A@account) of the client terminals T connected to the same LAN. Reference numeral  103  denotes identification data indicating a post of the corresponding client terminal T, such as “sales division” and “development division.” 
     As described above, the relay group information  100  are created to be distinguished from the other relay group information and includes a group of relay account information  102  permitting access to each other. The relay account information  102  includes the accounts of the relay servers R and the accounts of the client terminals T disposed in the same LAN as the relay server R is disposed and registered in the corresponding relay server. Accordingly, referring to the relay group information  100 , the LANs constituting the same group and the relay servers R or the client terminals T registered in the respective LANs can be seen. 
     Shared Resource Information 
     Details of the shared resource information  120  are shown in  FIG. 7 .  FIG. 7  illustrates the shared resource information  120  stored in the shared resource information DB  604  of the client terminal  1 A. The same information as the shared resource information  120  is also stored in the shared resource information DB  506  of the relay server R 1  registered in the same LAN as the client terminal  1 A is disposed. The shared resource information  120  includes account identification information  121  indicating the shared resource information  120  associated with the client terminal  1 A and individual shared resource information  122  associated with the client terminal  1 A. 
     The account identification information  121  is information for identifying the shared resource information  120  of each client terminal. 
     The individual shared resource information  122  includes shared resource identification information  123 , family account information  124 , and family resource information  125 . 
     The shared resource identification information  123  is information for identifying the individual shared resource information  122 . A different ID is given to the individual shared resource information  122  every time of creation thereof and the individual shared resource information is easily identified. Here, the shared resource identification information  123  includes an ID (for example, 20061001150032user1A@relay—server1) correlated with the client terminal T having requested for creation of the shared resource information  120  and a name (for example, use1A—policy01) for facilitating the identification thereof. 
     Accordingly, since users can specify the individual shared resource information  122  by the use of the shared resource identification information  123 , it is possible to easily edit the details thereof or the like. 
     The family resource information  125  is a set of resource information  126  indicating essences of the resources such as files or folders held by the client terminal T. The resource information  126  includes information (for example, resource name=“folderA”) indicating names of essences of the shared resources, information (for example, owner=“user1A@account”) indicating the accounts of the client terminal T (owner client terminal) which can operate the essence of the resource, and information (for example, value=“c:/folderA”) indicating a position of the essence of the resource. 
     The family account information  124  is a set of accounts (for example, user1A@account) of the client terminals T sharing the essence of the resource indicated by the family resource information  125 . The family account information  124  includes the owner client terminal T and the client terminals T (user client terminals) which can operate the essence of the resource indirectly through the owner client terminal. The user client terminals T are client terminals which cannot directly operate the essence of the resource but can indirectly operate the resource through the owner client terminal T. 
     A flow of a communication process in the relay communication system having the above-mentioned configuration will be described with reference to the process sequence diagrams shown in  FIGS. 8 ,  9 ,  11 ,  15 , and  18 . Steps S 1  to S 9  shown in  FIG. 8  show a step of registering the accounts of devices. 
     The relay server R 1  transmits a request for registration of an account (REGISTER) to the external server S (step S 1 ). Here, the relay server R 1  gives a request for registration of its account (sip: relay—server1@net). The external server S returns an OK response to the relay server R 1  and registers the account of the relay server R 1  and a global IP address of the relay server R 1  in the relay server account information DB  203  so as to be correlated with each other. 
     Subsequently, the relay server R 2  transmits a request for registration of an account (REGISTER) to the external server S (step S 2 ). Here, the relay server R 2  gives a request for registration of its account (sip: relay—server2@net). The external server S returns an OK response to the relay server R 2  and registers the account of the relay server R 2  and a global IP address of the relay server R 2  in the relay server account information DB  203  so as to be correlated with each other. 
     Similarly, the relay server R 3  transmits a request for registration of its account (REGISTER) to the external server S and registers its account in the external server S (step S 3 ). 
     The client terminal  2 A transmits a request for registration of an account (REGISTER) to the relay server R 2  (step S 4 ). Here, client terminal  2 A gives a request for registration of its account (sip: user2A@account). The relay server R 2  returns an OK response and registers the account of the client terminal  2 A and a private IP address of the client terminal  2 A in the account information DB  504  so as to be correlated with each other. 
     Subsequently, the client terminal  1 A transmits a request for registration of an account (REGISTER) to the relay server R 1  (step S 5 ). Here, client terminal  1 A gives a request for registration of its account (sip: user1A@account). The relay server R 1  returns an OK response and registers the account of the client terminal  1 A and a private IP address of the client terminal  1 A in the account information DB  504  so as to be correlated with each other. 
     Similarly, the client terminal  3 A transmits an account registering request to the relay server R 3  (step S 6 ) and the client terminal  2 B transmits an account registering request to the relay server R 2  (step S 7 ). The client terminal  1 B transmits the account registering request to the relay server R 1  (step S 8 ) and registers the account in the relay server R. The client terminal  3 B transmits the account registering request to the relay server R 3  (step S 9 ) and registers the account in the relay server R. 
     In these steps, the registration of the accounts of the relay servers R in the external server S is ended and the registration of the accounts of the client terminals T in the relay servers R is ended. 
     The above-mentioned order of steps is an example and any order may be used as long as the registration of the accounts of the devices is ended. The devices cannot participate in the relay communication system, when the devices exist in the network but do not finish the registration of the accounts thereof and is not connected to the network. For example, the LAN 4  shown in  FIG. 1  cannot participate in the communication service described here, because it has not finished the registration of the accounts and is not connected to the network. 
     Steps S 10  to S 16  show in  FIG. 9  show a communication step between the relay servers R. The processes of steps S 1  to S 16  are generally carried out as an initial setting for a network by a user or an operator. 
     The relay server R 1  transmits a connection request command (INVITE method) for the relay server R 2  to the external server S (step S 10 ). In the INVITE method, an account (sip: relay-server2@net) of the relay server R 2  of a connection destination. The external server S acquires the global IP address of the relay server R 2  by referring to the relay server account information DB  203 . The external server S relays the INVITE method transmitted from the relay server R 1  to the relay server R 2 . After the connection request command is transmitted from the relay server R 1  to the relay server R 2 , the OK response is transmitted from the relay server R 2  to the relay server R 1  through the external server S. 
     In this way, the communication process between the relay servers R is performed via the external server S. Since the communication process between the relay servers R is performed via the external server S in any communication, the specific description of the communication process via the external server S is omitted in the following description. 
     Then, the relay server R 1  performs a change notification setting process using a notification event between the relay server R 1  and the relay server R 2  by the use of a SUBSCRIBE method to the relay server R 2  (step S 11 ). Accordingly, every when details of the relay group information  100  stored in the relay server R 2  is changed, the changed information is transmitted from the relay server R 2  to the relay server R 1  by the use of the NOTIFY method. 
     The SUBSCRIBE method is one processing unit defined in the SIP. When a notification even is set by the use of the SUBSCRIBE method, changed information is exchanged during the period when the notification event can be executed. That is, every when predetermined information of the device having received the SUBSCRIBE method is changed, new information is notified to the device having transmitted the SUBSCRIBE method by the use of the NOTIFY method. 
     Similarly, on the contrary, the relay server R 2  performs the change notification setting process between the relay server R 2  and the relay server R 1  by the use of the SUBSCRIBE method to the relay server R 1  (step S 12 ). Accordingly, even when details of the relay group information  100  stored in the relay server R 1  is changed, the changed information is transmitted from the relay server R 1  to the relay server R 2  by the use of the NOTIFY method. 
     Here, since the change notification setting process is first performed, the party having received the SUBSCRIBE method performs a notification process and the relay server R of the party having transmitted the SUBSCRIBE method creates new relay group information  100   a.    
     The relay group information  100   a  is shown in  FIG. 10 . Here, since the relay server R 1  and the relay server R 2  form a group, both relay account information  102   a  and  102   b  is include in the relay group information  100   a . That is, the relay account information  102   b  of the relay server R 2  is notified in the NOTIFY method of step S 11 . The relay account information  102   a  of the relay server R 1  is notified in the NOTIFY method of step S 12 . By exchanging the information, the relay group information  100   a  having the same details is created by both parties. The created relay group information  100   a  is stored in the relay group information DB  505 . 
     In step S 13 , the relay server R 3  is newly added to the relay group formed between the relay server R 1  and the relay server R 2 . Specifically, an operator or the like specifies a group with reference to the group identification information  101 . The relay server R 2  transmits a connection request command (INVITE method) to the relay server R 3  on the basis of the operator&#39;s operation or the like (step S 13 ). In response to the transmission, their relay server R 3  transmits an OK response to the relay server R 2 . Similarly to steps S 11  and S 12 , a change notification setting process using the SUBSCRIBE method is performed between the relay servers R 2  and R 3  (steps S 14  and S 15 ). The changed information is transmitted by the use of the NOTIFY method and new relay group information  100   b  is created. 
     Here, the relay group information having the same details as the relay group information shown in  FIG. 6  is created. As shown in  FIG. 6 , since three relay servers R 1 , R 2 , and R 3  form one group, the relay group information  100   b  includes relay account information  102   a ,  102   b , and  102   c . That is, the relay account information  102   c  of the relay server R 3  is notified in the NOTIFY method of step S 14 . The relay account information  102   a  and  102   b  stored in the relay server R 2  is notified in the NOTIFY method of step S 15 . By exchanging the information, the relay group information  100   b  having the same details is created by both parties. The new relay group information  100   b  is stored in the respective relay group information DBs  505 . 
     The relay group information  100  which the relay server R 2  stores in the relay group information DB  505  is changed due to step S 14 . As a result, the changed information is transmitted to the relay server R 1  (step S 16 ) on the basis of the change notification setting process of step S 11 . Specifically, the relay account information  102   c  of the relay server R 3  is transmitted to the relay server R 1  and the relay group information  100   b  shown in  FIG. 6  is created and stored. 
     In this way, when any relay group information  100  is changed, the changed details are automatically updated between the relay server R 1  and the relay server R 2  and between the relay server R 2  and the relay server R 3 . Accordingly, even when the account of the relay server R or the client terminal T is changed, it is possible to dynamically cope with the change. Of course, the relay group information  100  can be formed between arbitrary relay servers R and may be plural. 
     A flow of the communication process of sharing resources will be described with reference to the sequence diagrams of  FIGS. 11 and 15 . 
     In  FIG. 11 , the client terminal  1 A transmits an account information transmitting request (GetAccountList command) to the relay server R 1  (step S 21 ). In response to the request, the relay server R 1  transmits the details of the relay group information stored therein, that is, the relay account information  102 , to the client terminal  1 A so as to display the transmitted relay group information on the client terminal  1 A. The relay account information  102  is displayed in the client terminal  1 A. With the client terminal  1 A, the user selects and designates the user client terminals T sharing the resource with reference to the relay account information  102 . Here, the user client terminals  2 A and  3 A are designated. 
     The designated client terminal  1 A transmits a shared resource creating request (CreateSharedResource command) including the information to the relay server R 1  (step S 22 ). The relay server R 1  having received the shared resource creating request stores the created shared resource information  120  in its shared resource information DB  506 . The relay server R 1  transmits the created shared resource information  120  to the relay servers R 2  and R 3  connected to the designated user client terminals  2 A and  3 A by the use of the NOTIFY method (steps S 22 . 1  and S 22 . 2 ). The notified relay servers R 2  and R 3  store the shared resource information  120  in their shared resource information DB  506 . Then, the relay servers R 2  and R 3  transmits a shared resource changing request (UpdateSharedResource command) to the designated user client terminals  2 A and  3 A (steps S 22 . 1 . 1  and S 22 . 2 . 1 ). The notified user client terminals  2 A and  3 A change the shared resource information  120  stored in their shared resource information DB  604 . 
     The shared resource information  120   a  stored in the relay servers R 1 , R 2 , and R 3  and the client terminals  1 A,  2 A, and  3 A in steps S 22  to  522 . 2 . 1  after a series of processes of step S 22  is performed is shown in  FIG. 12 . The shared resource information  120   a  includes shared resource identification information  121  for identifying the shared resource information  120   a  at a glance. The shared resource information  120   a  includes family account information  124  which is a set of the account of the owner client terminal  1 A and the accounts of the designated user client terminals  2 A and  3 A. 
     The process of adding the resource information  126  indicating essences of the shared resources to the shared resource information  120  is performed by a user&#39;s operation using the client terminal  1 A. That is, the user selects an essence of a shared resource among essences of resources operable by the client terminal  1 A and designates the essence of the selected resource with the client terminal  1 A. Here, “folderA”, “file001.xls”, “file002.wrd”, and “file003.pdf” are designated. 
     The designated client terminal  1 A transmits a shared resource changing request (UpdateSharedResource command) including the designated information to the relay server R 1  (step S 23 ). The relay server R 1  having received the shared resource changing request stores the changed shared resource information  120   b  in its shared resource information DB  506 . The relay server R 1  transmits the changed shared resource information  120   b  to the relay servers R 2  and R 3  connected to the user client terminals  2 A and  3 A by the use of the NOTIFY method (steps S 23 . 1  and S 23 . 2 ). The notified relay servers R store the shared resource information  120   b  in its shared resource information DB  506 . The relay servers transmit the shared resource changing request (UpdateSharedResource command) to the user client terminals  2 A and  3 A (steps S 23 . 1 . 1  and S 23 . 2 . 1 ). The user client terminals  2 A and  3 A having received the request change the shared resource information  120  stored in their shared resource information DB  604 . 
     The shared resource information  120   b  stored in the relay servers R and the client terminals T after the processes of step S 23  are performed is shown in  FIG. 13 . In the shared resource information  120   b , family resource information  125   a  is added to the shared resource information  120   a  created in step S 22 . 
     Referring to the shared resource information  120   b  created by the above-mentioned communication processes, it can be specified that the client terminal  1 A is the owner client terminal and that the client terminals  2 A and  3 A are the user client terminals T. The details of the essences of the resources which can be operated by the owner client terminal  1 A and the locations thereof in the network can be specified with reference to the shared resource information  120   b.    
     A step of allowing the client terminal  2 B to newly perform a process of creating the shared resource information  120  is described now. 
     The client terminal  2 B transmits an account information transmitting request (GetAccountList command) to the relay server R 2  (step S 24 ). In response to the request, the relay server R 2  transmits the details of the relay group information  100  stored therein, that is, the relay account information  102 , to the client terminal  2 B to display the transmitted information on the client terminal  2 B. The relay account information  102  is displayed in the client terminal  2 B. With the client terminal  1 A, the user selects and designates the user client terminals T sharing the resource with reference to the relay account information  102 . Here, the client terminals  1 A and  3 B are designated as the user client terminals. 
     The designated client terminal  2 B transmits a shared resource creating request (CreateSharedResource command) including the information to the relay server R 2  (step S 25 ). The relay server R 2  having received the shared resource creating request stores the created shared resource information  120  in its shared resource information DB  506 . The relay server R 2  transmits the created shared resource information  120  to the relay servers R 1  and R 3  connected to the designated user client terminals  1 A and  3 B by the use of the NOTIFY method (steps S 25 . 1  and S 25 . 2 ). The relay servers R 1  and R 3  having received the notification store the created shared resource information  120  in their shared resource information DB  506 . Then, the relay servers R 1  and R 3  transmits a shared resource changing request (UpdateSharedResource command) to the designated user client terminals  1 A and  3 B (steps S 25 . 1 . 1  and S 25 . 2 . 1 ). The user client terminals  1 A and  3 B having received the changing request change the shared resource information  120  stored in their shared resource information DB  604 . 
     Shared resource information  120   c  stored in the relay servers R 1  and the client terminal  1 A is shown in  FIG. 14 . In the shared resource information  120   c , newly created individual shared resource information  122   a  is added to the shared resource information  120   b  created in step S 23 . New shared resource identification information  123   a  is given to the newly created individual resource information  122   a.    
     Since client terminals  2 B and  3 B are not associated with the shared resource information  120   b  previously created, the newly created individual shared resource information  122   a  is stored as the shared resource information  120  in the client terminals  2 B and  3 B and the relay servers R 2  and R 3 . 
       FIG. 15  shows a flow of a communication process when a process of adding the resource information  126  of the resource shared by the client terminal  1 A to the newly created individual shared resource information  122   a  is performed. 
     The user selects the individual shared resource information  122   a  to which the resource is added among the shared resource information  120   c  on the basis of the shared resource identification information  123   a  and designates the selected information with the client terminal  1 A. The user selects a shared resource among the essences of the resources which can be operated by the client terminal  1 A and designates the selected resource with the client terminal  1 A. Here, “file005.ppt” is designated. 
     The designated client terminal  1 A transmits a shared resource changing request (UpdateSharedResource command) including the designated information to the relay server R 1  (step S 26 ). The relay server R 1  having received the shared resource changing request stores the changed shared resource information  120   d  in its shared resource information DB  506 . The relay server R 1  transmits the changed individual shared resource information  122   a  to the relay servers R 2  and R 3  connected to the user client terminals T ( 2 B and  3 B) contained in the family account information  124  of the individual shared resource information  122   a  as a target by the use of the NOTIFY method (steps S 26 . 1  and S 26 . 2 ). The notified relay servers R 2  and R 3  change and store the shared resource information  120  in its shared resource information DB  506 . The relay servers transmit the shared resource changing request (UpdateSharedResource command) to the user client terminals  2 B and  3 B (steps S 26 . 1 . 1  and S 26 . 2 . 1 ). The user client terminals  2 B and  3 B having received the request change the shared resource information  120  stored in their shared resource information DB  604 . 
     The shared resource information  120   d  stored in the relay server R 1  and the client terminal  1 A is shown in  FIG. 16 . In the shared resource information  120   d , family resource information  125   b  is added to the individual shared resource information  122   a  of the shared resource information  120   c  created in step S 25 . The changed shared resource information  122   a  is stored as the shared resource information  120  in the client terminals  2 B and  3 B and the relay servers R 2  and R 3 . 
     A flow of a communication process when a process of adding the resource information  126  to the shared resource information  120  is performed on the individual shared resource information  122   a  by the client terminal  2 B is then shown. 
     The user selects the individual shared resource information  122   a  to which the resource is added among the shared resource information  120  on the basis of the shared resource identification information  123   a  and designates the selected information with the client terminal  2 B. The user selects a shared resource among the essences of the resources which can be operated by the client terminal  2 B and designates the selected resource with the client terminal  2 B. Here, “folderC”, “file00A.ppt”, “file00B.ppt” are designated. 
     The designated client terminal  2 B transmits a shared resource changing request (UpdateSharedResource command) including the designated information to the relay server R 2  (step S 27 ). The relay server R 2  having received the shared resource changing request stores the changed shared resource information  120  in its shared resource information DB  506 . The relay server R 2  transmits the changed individual shared resource information  122  to the relay servers R 1  and R 3  connected to the user client terminals  1 A and  3 B sharing the resource by the use of the NOTIFY method (steps S 27 . 1  and S 27 . 2 ). The notified relay servers R 1  and R 3  change and store the shared resource information in its shared resource information DB  506 . The relay servers transmits the shared resource changing request (UpdateSharedResource command) to the user client terminals  1 A and  3 B (steps S 27 . 1 . 1  and S 27 . 2 . 1 ). The user client terminals  1 A and  3 B having received the request change the shared resource information  120  stored in their shared resource information DB  604 . 
     The shared resource information  120   e  stored in the relay server R 1  and the client terminal  1 A is shown in  FIG. 17 . In the shared resource information  120   e , family resource information  125   c  is added to the shared resource information  120   d  created in step S 26 . The changed individual shared resource information  122   a  is stored as the shared resource information  120  in the client terminals  2 B and  3 B and the relay servers R 2  and R 3 . 
     In this way, the client terminals T can form a set of client terminals sharing the resources. The client terminals T can change the shared resources by a desired amount as needed and thus can constitute a relay communication system which is excellent in expansibility and flexibility. 
       FIG. 18  shows a flow of a communication process of allowing a client terminal T in a LAN to indirectly operate a resource held by a client terminal T in a different LAN over the Internet. 
     The first process shows a flow when the client terminal  2 A in the LAN 2  indirectly copies a resource held and operated by the client terminal  1 A in the LAN 1 . 
     The client terminal  2 A transmits a copy request (Copyfile command) to the relay server R 2  when receiving an instruction to copy “file003.pdf” from a user (step S 31 ). The relay server R 2  having received the copy request selects the owner client terminal T holding “file003.pdf” as a copy target on the basis of the shared resource information  120 . The relay server R 2  selects the relay server R connected to the owner client terminal T on the basis of the relay group information  100  and communicates with the selected relay server. Of course, when the resource is not shareable or when the account is not registered, the communication is not made. 
     Subsequently, the relay server R 2  transmits a connection request (INVITE method) to the selected relay server R 1  through the external server S (step S 31 . 1 ). The relay server R 1  having received the connection request transmits a copy request to the client terminal  1 A (step S 31 . 1 . 1 ). The client terminal  1 A having received the copy request transmits an OK response to the relay server R 1  when it can operate the resource (file003.pdf) as a target. The relay server R 1  transmits the OK response to the relay server R 2 . 
     The relay server R 2  having received the OK response transmits a Mediasession command to the relay server R 1  and a communication passage is established between the relay servers R 1  and R 2  (step S 31 . 2 ). The relay server R 1  having received the Mediasession command transmits a GetFileData command for copying a file to the client terminal  1 A to request for copying a file (step S 31 . 2 . 1 ). The client terminal  1 A having received the file copy request copies “file003” as a target from the resource storing unit  603  and transmits the copied file to the relay server R 1 . “file003” is transmitted to the client terminal  2 A through the relay server R 1  and the relay server R 2  (FileTransfer command). The essence of the resource may be copied from the file server F, as well as the resource storing unit  603 . 
     When a series of communication processes are finished, a cutting request (BYE method) is transmitted from the relay server R 2  to the relay server R 1  so as to cut the established communication path, thereby cutting the communication path and ending the communication between both relay servers (step S 32 ). 
     The next flow is a flow when the client terminal  3 B in the LAN  3  indirectly deletes an operable resource which is held by the client terminal  2 B in the LAN 2 . 
     When receiving an instruction for deleting “file00A.ppt” from a user, the client terminal  3 B transmits a Deletefile command for deleting a file to the relay server R 3  to request for the deletion (step S 33 ). The relay server R 3  having received the deleting request specifies the owner client terminal T holding and operating “file00A.ppt” as a deletion target and a relay server R connected to the owner client terminal T on the basis of the shared resource information  120  and the relay group information  100 . 
     The relay server R 3  transmits information on the deleting request to the specified relay server R 2  through the external server S by the use of the NOTIFY method (step S 33 . 1 ). The relay server R 2  having received the information on the deleting request transmits a Deletefile command to the client terminal  2 B to request for the deletion (step S 33 . 1 . 1 ). The client terminal  2 B having received the deleting request deletes the resource (file00A.ppt) as a target from the resource storing unit  603 . An OK response is transmitted to the client terminal  3 B through the relay server R 2  and the relay server R 3 . 
       FIG. 19  shows shared resource information  120   f  after the deletion process is performed. As shown in  FIG. 19 , the resource information  126  of “file00A.ppt” as a deletion target is deleted from the shared resource information  120 . The essence of the resource is deleted. 
     When an operation of changing the details of the shared resource information  120  such as the deletion of a resource has been performed, a process of updating the shared resource information is subsequently performed. 
     Specifically, the client terminal  3 B having been instructed to perform an operation accompanying the change of the shared resource information  120  transmits a shared resource changing request (UpdateSharedResource command) to the relay server R 3  (step S 34 ). The relay server R 3  having received the changing request transmits the changed shared resource information  120  to the relay servers R 1  and R 2  associated with the changed shared resource information  120  by the use of the NOTIFY method (steps S 34 . 1  and S 34 . 2 ). The relay servers R 1  and R 2  update and store the shared resource information in their shared resource information DB  506 . 
     Then, the relay servers transmit the shared resource changing request (UpdateSharedResource command) to the user client terminals  1 A and  2 B associated with the changed shared resource information  120  (steps S 34 . 1 . 1  and S 34 . 2 . 1 ). The user client terminals  1 A and  2 B having received the changing request changes the shared resource information stored in their shared resource information DB  604 . 
     That is, when the shared resource information  120  is changed, the fact is notified to the relevant relay servers R and the relevant client terminals T and the shared resource information  120  is updated at once. 
     Second Embodiment 
     A second embodiment of the invention provides a relay communication system which can dynamically cope with an unexpected trouble or a case where an access status of a relay server R or a client terminal T varies. 
     Elements of a relay communication system such as relay servers R and client terminals T and basic configurations of communication processes are equal to those of the first embodiment. This embodiment will be described in detail with reference to the flowchart of  FIG. 20  and the sequence diagram of  FIG. 21   
       FIG. 20  shows operation checking processes which are performed by the relay servers R.  FIG. 21  shows a communication flow processed in the relay communication system at the time of performing the operation checking processes. In  FIG. 21 , the relay server R 1  checks operations of the relevant relay servers R and an access trouble occurs in the relay server R 3 . In addition, in  FIG. 21 , the relay server R 1  and the relay server R 2  check operations of the client terminals T and an access trouble occurs in the client terminal  2 B. 
       FIG. 22  shows the relay group information  100  stored in the relay server R 1  before starting the process steps shown in  FIG. 21 .  FIG. 23  shows the shared resource information  120  stored in the relay server R 1  and the client terminal  1 A before starting the process steps shown in  FIG. 21 . Unlike the first embodiment, the information  100  and  120  according to this embodiment contains status information (status)  107  and  127 , respectively. For example, “status=‘ok’” or “status=‘logon’” indicates that the displayed relay server R, client terminal T, or resource is accessible. 
     Steps S 110  and S 111  shown in  FIG. 20  show a process using a timer. That is, the relay servers R according to this embodiment have a timer function (not shown) and have an unit for executing a predetermined program at a constant time interval corresponding to a user&#39;s time setting. 
     Specifically, a processing interval (time) of a program is set by an operator (step S 110 ). When the timer is counted and reaches a predetermined time, a series of processes of checking an operation are preformed (step S 111 ). That is, when the timer reaches a predetermined time, a process of reading the relay group information from the relay group information DB  505  is performed (step S 112 ). Then, until the operations of all the relay servers R stored in the relay group information  100  are completely checked, the operation checking process is repeatedly performed (step S 113 ). 
     At the time of checking the operations, an operation check request for checking whether they are accessible is transmitted to different relay servers R stored in the read relay group information  100  (step S 114 ). Then, it is checked whether a response is returned (step S 115 ). When it is checked that a response is returned, it is checked that it is accessible. When it is checked that a response is not returned, it is checked that it is not accessible and the relay group information  100  stored therein is updated (step S 116 ). 
     For example, in  FIG. 21 , the relay server R 1  performs the operation checking process on the relay servers R 2  and R 3  constituting a relay group. That is, the relay server R 1  transmits a MESSAGE method to the relay server R 2  (step S 101 ). The relay server R 2  having received the MESSAGE method returns an OK response to the relay server R 1  as a transmission source (YES in step S 115  of  FIG. 20 ). As a result, the relay server R 1  checks that the relay server R 2  is accessible. 
     Similarly, the relay server R 1  transmits the MESSAGE method to the relay server R 3  (step S 102 ). The relay server R 3  does not return the OK response to the relay server R 1  as a transmission source and transmits no response. That is, the relay server R 3  is inaccessible because it is powered off or downed for a certain reason. Thus, the relay server R 1  checks that the relay server R 3  is inaccessible (NO in step S 115  of  FIG. 20 ). In this case, the relay server R 1  updates details of the relay group information  100  stored therein (step S 116  of  FIG. 20 ). 
     In  FIG. 20 , when the series of processes of checking an operation is finished, the relay server R checks whether the relay group information  100  has been updated (step S 117 ). When it is checked that the relay group information  100  has been updated, a change notification of the relay group information  100  is transmitted to the relevant relay servers R (step S 118 ). 
     Specifically, as shown in  FIG. 21 , the change notification of the relay group information  100  is transmitted from the relay server R 1  to the relay server R 2  by the use of the NOTIFY method (step S 103 ). 
     The details of the transmitted change notification are shown in  FIG. 24 . As shown in  FIG. 24 , “error” indicating that it is inaccessible is written in the status information (status)  107   a  of the inaccessible relay server R 3 . The relay server R 2  having received the change notification updates the details of the relay group information  100  stored therein on the basis of the change notification. 
     Subsequently, a process of updating the shared resource information  120  is performed (step S 119 ). 
     For example, in  FIG. 21 , since the relay server R 3  is inaccessible, the resource of which the owner is a client terminal T (for example,  3 A) registered in the relay server R 3  cannot be operated. Accordingly, the relay server R 1  updates the corresponding data of the shared resource information  120  stored therein on the basis of the details of the updated relay group information  100 . The relay server R 2  also updates the corresponding data of the shared resource information  120 . 
     The relay servers R 1  and R 2  transmits the change notification of the shared resource information  120  to the relevant client terminals T stored in their account information DB  504  (step S 120 ). The relevant client terminals T are client terminals T written in the family account information  124  of the shared resource information  120  containing the resources of which an access status has been updated. Specifically, in  FIG. 21 , the relay server R 2  transmits a shared resource updating request (UpdateSharedResource command) to the client terminal  2 A (step S 103 . 1 ). Similarly, the relay server R 1  transmits the shared resource updating request (UpdateSharedResource command) to the client terminal  1 A (step S 104 ) 
     The details of the change notification transmitted in step S 103  are shown in  FIG. 25 . As shown in the figure, “error” indicating that it is inaccessible is written in the status information (status)  127   a  of a resource “file003.pdf”, the owner of which is the client terminal  3 A connected to the relay server  3 . The client terminals  1 A and  2 A having received the change notification update the details of the shared resource information  120  stored therein on the basis of the change notification. 
     In this way, the relay server R periodically checks operations of the different relay servers R, updates the relevant information when the access status is changed, and transmits the resultant information to the relevant relay servers R. 
     The relay server R performs the operation checking process on the client terminals T, which are connected to the same LAN and stored in the account information DB  504  thereof. 
     As shown in  FIG. 20 , the relay server R periodically performs the operation checking process by the use of the timer function. Since steps S 130  and S 131  are equal to steps S 110  and S 111  described above, description thereof is omitted. 
     When the timer reaches a predetermined time, a process of reading the account information of the client terminals T stored in the account information DB  504  (step S 132 ). Then, until the operation checking process on all the client terminals T stored in the account information DB  504  is finished, the operation checking process is repeatedly performed (step S 133 ). 
     In operation checking process, an operation checking request for checking whether they are accessible is transmitted to the client terminals T stored in the account information DB  504  (step S 134 ). Then, it is checked whether a response is returned (step S 135 ). When it is checked that a response is returned, it is checked that it is accessible. When it is checked that a response is not returned, it is checked that it is inaccessible and the corresponding information stored in the relay group information DB  505  is updated (step S 136 ). 
     For example, in  FIG. 21 , the relay server R 1  performs the operation checking process on the client terminals  1 A and  1 B stored in the account information DB  504  thereof. That is, the relay server R 1  transmits a checking request command (Confirmation) to the client terminal  1 A (step S 105 ). The client terminal  1 A having received the checking request command returns a response to the relay server R 1  as a transmission source (YES in step S 135  of  FIG. 20 ). As a result, the relay server R 1  checks that client terminal  1 A is accessible. Similarly, the relay server R transmits a checking request command to the client terminal  1 B to check that it is accessible (step S 107 ). 
     The relay server R 2  also performs the operation checking process and transmits the checking request command to the client terminal  2 A stored in the account information DB  504  of the relay server R 2  to check that it is accessible (step S 106 ). 
     Similarly, the relay server R 2  transmits the checking request command to the client terminal  2 B (step S 108 ). The client terminal  2 B does not return a response and transmits no response. That is, the client terminal  2 B is inaccessible because it is powered off or logged-off or downed for a certain reason. Thus, the relay server R 2  checks that the client terminal  2 B is inaccessible (NO in step S 135  of  FIG. 20 ). In this case, the relay server R 2  updates details of the relay group information  100  stored therein (step S 136  of  FIG. 20 ). 
     In  FIG. 20 , when the series of processes of checking an operation is finished, the relay server R checks whether the relay group information  100  has been updated (step S 137 ). When it is checked that the relay group information  100  has been updated, a change notification of the relay group information  100  is transmitted to the relevant relay servers R (step S 138 ). 
     Specifically, as shown in  FIG. 21 , the change notification of the relay group information  100  is transmitted from the relay server R 2  to the relay server R 1  by the use of the NOTIFY method (step S 109 ). Since the relay server R 3  is inaccessible, the change notification is not transmitted to the relay server R 3 . 
     The details of the transmitted change notification are shown in  FIG. 26 . As shown in  FIG. 26 , “logoff” indicating that it is inaccessible is written in the status information (status)  107   b  of the inaccessible client terminal  2 B. The relay server R 1  having received the change notification updates the details of the relay group information  100  stored therein on the basis of the change notification. 
     Subsequently, similarly to the previous step S 119 , a process of updating the shared resource information  120  is performed. This is because the client terminal  2 B is inaccessible and thus the resource of which the owner is the client terminal  2 B cannot be operated. The relay server R 2  updates the corresponding data of the shared resource information  120  stored therein on the basis of the details of the updated relay group information  100 . The relay server R 1  similarly updates the corresponding data of the shared resource information  120 . 
     Similarly to the previous step S 120 , the relay servers R 1  and R 2  transmits the change notification of the shared resource information  120  to the relevant client terminals T (here, the client terminal  1 A). 
     Specifically, in  FIG. 21 , the relay server R 1  transmits the shared resource updating request (UpdateSharedResource command) to the client terminal  1 A (step S 109 . 1 ) 
     The details of the change notification transmitted here are shown in  FIG. 27 . As shown in  FIG. 27 , “error” indicating that it is inaccessible is written in the status information (status)  127   b  of resources “folderC”, “file00A.ppt”, and “file00B.ppt”, the owner of which is the accessible client terminal  2 B. The client terminal  1 A having received the change notification updates the details of the shared resource information  120  stored therein on the basis of the change notification. 
     In this way, the relay server R periodically checks the operations of the client terminals registered therein, updates the relevant information when the access status is changed, and transmits the resultant information to the relevant relay servers R. 
     After the inaccessibility is checked and then a series of updating processes are performed, the access status may be restored. In this case, in the operation checking process after the restoration, the status information (status)  107  and  127  is updated from the details indicating the inaccessibility to the details indicating the accessibility by means of the same processes as the inaccessible case. 
     As described above, in the relay communication system according to this embodiment, the relay group information  100  and the shared resource information  120  held in the relay communication system are always updated to the latest information by the relay servers R. Accordingly, even when the relay servers R are powered off or logged off or an unexpected trouble occurs therein, the statuses can be easily grasped, thereby not confusing the user. 
     Third Embodiment 
     A third embodiment of the invention provides a more dynamic relay communication system which can use the resources without any consciousness, since it does not require troublesome works such as a change of set conditions even when a client terminal T having been registered in a LAN moves to a different LAN. 
     Elements of a relay communication system such as relay servers R and client terminals T and basic configurations of communication processes are equal to those of the first embodiment. This embodiment will be described in detail with reference to the sequence diagrams of  FIGS. 28 and 29 . 
       FIGS. 28 and 29  show flows of a communication process when a client terminal T having been registered in a LAN moves to and accesses a different LAN. Specifically, the client terminal  1 A registered in the relay server R 1  of the LAN 1  is logged off and is logged in the relay server R 2  of the LAN 2 . 
       FIG. 30  shows the details of the relay group information  100  stored in the relevant relay servers R 1 , R 2 , and R 3  before the client terminal  1 A moves.  FIG. 31  shows the details of the shared resource information  120  stored in the client terminals  1 A,  2 A, and  3 A and the relay servers R 1 , R 2 , and R 3  which constitute a share group before the client terminal  1 A moves. 
     In  FIG. 31 , for example, value=‘//network/z:folderZ’” is written in the address information indicating a location of a resource essence having a name of “folderNet”. This means that the resource essence having the name “folderNet” is located in a storage unit on the network of the LAN 1  different from the client terminal  1 A. In this embodiment, it is assumed that “folderZ” is located in the file server F disposed in the LAN 1 . On the other hand, “value=‘c:/folderA’” and the like is located in a storage unit built in the client terminal  1 A. 
     Unlike the first embodiment, the information  100  and  120  according to this embodiment contains status information (status)  107  and  127 , respectively, indicating access statuses of the relay server R, client terminal T, and resource. For example, “status=‘ok’” or “status=‘logon’” indicates that the displayed relay server R, client terminal T, or resource is accessible. 
     Access information (server)  108  indicating the relay server R connected to the corresponding client terminal at that time is written in the relay group information  100  according to this embodiment every client terminal T. For example, “server=‘relay-server1’” indicates that an access destination at that time is the relay server R 1 . 
       FIG. 28  is referred to. The client terminal  1 A which is disposed in the LAN 1  as shown in  FIG. 1  and which is registered in advance in the relay server R 1  as shown in  FIG. 30  transmits a logoff request (REGISTER) to the relay server R 1  (step S 201 ). The relay server R 1  having received the request returns a response to the client terminal  1 A having transmitted the request. 
     Since the client terminal  1 A is logged off, the details of the relay group information  100  is changed and the relay server R 1  updates the relay group information  100  stored therein. Then, the relay server R 1  transmits the change notification of the relay group information to the different relay servers R 2  and R 3  constituting a relay group including the client terminal  1 A by the use of the NOTIFY method (steps S 202  and S 203 ). The relay servers R 2  and R 3  having received the change notification update the relay group information  100  stored therein and returns a response to the transmission source. 
       FIG. 32  shows the details of the relay group information  100   h  transmitted and received with the change notification. As shown in  FIG. 32 , “logoff” indicating the inaccessibility is written in the status information  107   a  of the logged-off client terminal  1 A. Since the access to the relay server R 1  is cut off, “relay-server1” is deleted from the access information  108   a  indicating the relay server R as an access destination to be empty. 
     The details of the shared resource information are updated, since the client terminal  1 A is logged off. For example, a resource of which the owner is the client terminal  1 A cannot be operated since the client terminal  1 A is logged off. Accordingly, the relay server R 1  updates the corresponding data of the shared resource information  120  stored therein on the basis of the details of the updated relay group information  100 . 
     The relay server R 1  transmits the change notification of the shared resource information  120  to the different relay servers R in which the client terminals T associated with the update are registered. The client terminals T associated with the update mean client terminals T contained in the family account information  124  of the shared resource information  120  including a resource of which the access status is changed due to the update. Since the notification destination of this change notification is equal to that of the previous change notification of the relay group information  100 , this change notification is transmitted in the same way as steps S 202  and S 203 . 
     The relay servers R 2  and R 3  having received the change notification of the shared resource information  120  update the shared resource information  120  stored therein. A status changing request (UpdateResourceStatus command) is transmitted to the relevant client terminals  2 A and  3 A on the basis of the change notification (steps S 202 . 1  and  203 . 1 ). The client terminals  2 A and  3 A having received the status changing request update the shared resource information  120  stored therein and returns a response to the transmission source. 
       FIG. 33  shows the details of the shared resource information  120   h  transmitted and received at the time of update. As shown in  FIG. 33 , “error” indicating the inaccessibility is written in the status information  127   a  of a resource (for example, “folderA”) of which the owner is the logged-off client terminal  1 A. 
     Accordingly, the access status of a client terminal T can be easily determined with reference to the relay group information  100  and the access status of a resource can be easily determined with reference to the shared resource information  120 . 
     The logged-off client terminal  1 A moves to the LAN 2  and transmits an access request for logon (REGISTER) to the relay server R 2  (step S 204 ). The relay server R 2  having received the access request determines whether the client terminal  1 A having transmitted the access request is registered with reference to the information of the client terminal T stored in the account information registering unit  504  thereof. When it is determined that it is not registered, the relay server R 1  in which the client terminal  1 A having transmitted the access request is registered is specified on the basis of the relay group information  100 . The relay server R 2  does not accept the access request for logon, when it cannot acquire the information of the client terminal  1 A and thus cannot specify the relay server. The relay server accepts the access request for logon when the client terminal is registered therein. 
     The relay server R 2  inquires of the specified relay server R 1  whether the logon information such as an ID or a password received from the client terminal  1 A is correct by transmitting a check request (NOTIFY) (step S 204 . 1 ). The relay server R 1  having received the check request transmits the answer to whether the logon information of the client terminal  1 A is correct to the relay server R 2  by the use of the NOTIFY method, with reference to the relay group information  100  stored therein. The relay server R 2  having confirmed that the client terminal  1 A having transmitted the request for logon is valid transmits the OK response to the client terminal  1 A and accepts the logon request of the client terminal  1 A to permit the access thereto. 
     When it accepts the logon request of the client terminal  1 A, the relay server R 2  updates the relay group information  100  stored therein. As shown in  FIG. 29 , the change notification of the relay group information  100  to the relevant relay servers R 1  and R 3  by the use of the NOTIFY method (step S 205  and S 206 ). The relay servers R 1  and R 3  having received the change notification updates the relay group information  100  stored therein on the basis of the change notification and returns a response to the transmission source. 
       FIG. 34  shows the details of the relay group information  100   i  transmitted and received at the time of update. As shown in  FIG. 34 , “logon” indicating the accessibility is written in the status information  107   b  of the logged-on client terminal  1 A. Similarly, “relay-server2” indicating the relay server R 2  as a new access destination is written in the access information  108   b . Accordingly, referring to this information, it can be determined that the client terminal  1 A registered in the relay server R 1  of the LAN 1  moves to the LAN 2  and logs on the relay server R 2 . 
     The client terminal  1 A transmits a transmission request (GetResourceStatus command) for the shared resource information  120  associated with the client terminal  1 A to the logged-on relay server R 2  (step S 207 ). The relay server R 2  having received the transmission request transmits the corresponding shared resource information  120  to the client terminal  1 A. 
     The client terminal  1 A having received the shared resource information  120  automatically checks whether a resource of which the owner is the client terminal  1 A can be operated and updates the status information  127  of the shared resource information  120  on the basis of the check result. The client terminal  1 A transmits the status changing request (UpdateResourceStatus command) to the logged-on relay server R 2  on the basis of the updated shared resource information  120  (step S 208 ). 
     The relay server R 2  having received the status changing request updates the shared resource information  120  as a target stored therein. The relay server R 2  transmits the status changing request (UpdateResourceStatus command) to the client terminal T ( 2 A) which is registered therein and which is contained in the family account information  124  of the shared resource information  120  as a target (step S 208 . 1 ). The client terminal  2 A having received the status changing request updates the shared resource information  120  stored therein and returns a response to the transmission source. 
     The change notification of the shared resource information is transmitted to the relay servers R 1  and R 3  in which the client terminals T ( 1 A and  3 A) contained in the family account information  124  is registered (steps S 208 . 2  and S 208 . 3 ). The relay servers R 1  and R 3  having received the change notification update the shared resource information  120  stored therein. The relay server R 3  transmits the status changing request (UpdateResourceStatus command) to the client terminal  3 A (step S 208 . 3 . 1 ). The client terminal  3 A having received the status changing request updates the shared resource information  120  stored therein and returns a response to the transmission source. The relay server R 1  does not transmit the status changing request to the client terminal  1 A. This is because the client terminal  1 A logs on the relay server R 2  already. 
       FIG. 35  shows the details of the shared resource information  120   i  transmitted and received at the time of update. As shown in  FIG. 35 , the status information  127   b  in which the client terminal  1 A having moved is owner is changed from the inaccessibility (error) to the accessibility (ok). 
     However, since the client terminal  1 A is the owner but moves to the LAN 2 , the client terminal  1 A cannot operate the resource, for example, “folderNet”, stored in the folderZ of the file server F disposed on the network of the LAN 1 . Accordingly, the status information  127   c  still contains the inaccessibility (error). 
     The details of the relay group information  100  and the shared resource information  120  are sequentially updated in the relay communication system. Accordingly, even when a user moves to a different LAN and accesses the different LAN, the user can operate the resources as if it does not move. 
     As described above, in the relay communication system employing the relay server according to the invention, a client terminal in a different LAN can operate a resource held by a different client terminal over the WAN as if it holds the resource. 
     It is possible to dynamically cope with the case where a client terminal having been registered in a LAN moves to and is logged on a different LAN and to use the resources without any consciousness, since it does not require troublesome works such as a change of set conditions. 
     Fourth Embodiment 
     A fourth embodiment of the invention will be described now. Elements of a relay communication system such as relay servers R and client terminals T and basic configurations of communication processes are equal to those of the first embodiment. This embodiment will be described in detail with reference to  FIGS. 36 to 44 . 
     The controller  602  of the client terminal T performs a process of displaying the details of the shared resource information  120  in cooperation with the display unit  605 , in addition to the above-mentioned function. In response to a command for operating a resource, the controller  602  performs a process of determining whether the resource can be operated directly and a process of registering the shared resource information  120  in the relay server R. The controller  602  performs a process of checking whether an operable resource stored in the relay server R can be periodically accessed and a process of transmits the change notification of the shared resource information  120  to the relay server when it is checked that the resource is inaccessible. 
     An example of the shared resource information  120  is shown in  FIG. 36 .  FIG. 36  is a diagram illustrating the shared resource information  120  stored in the shared resource information DB  604  of the client terminal  1 A. The same shared resource information  120  is stored in the shared resource information DB  506  of the relay server R 1  registered in the client terminal  1 A. The shared resource information  120  includes account identification information  1221  indicating that it is the shared resource information  120  of the client terminal  1 A and individual shared resource information  122  associated with the client terminal  1 A. The individual shared resource information  122  includes shared resource identification information  123 , family account information  124 , and family resource information  125 . 
     The family resource information  125  is a set of resource information  126  indicating an essence of a resource such as a file or a folder held by the client terminal T. The resource information  126  includes name information (for example, resource name=“folderA”) indicating a name of the essence of the shared resource. The resource information  126  further includes owner information  128  (for example, owner=‘user1A@account’) indicating an account of the client terminal T (owner client terminal) which can directly operate the essence of the resource. The resource information  126  further includes address information  129  (for example, value=‘c:/folderA’) indicating a location of the essence of the resource and status information  127  (for example, status=‘ok’) indicating the access status of the resource. 
     The number of individual shared resource information  122  included in the shared resource information  120  shown in  FIG. 36  is one, but plural individual shared resource information  122  may be included therein. The individual shared resource information  122  can be freely created as needed. Accordingly, when the details of the family account information  124  and the family resource information  125  are different, the individual shared resource information is individually created. 
     By referring to the shared resource information  120  having the above-mentioned configuration, it is possible to specify the client terminal T sharing a resource and to see the type or location of the resource. 
     The shared resource information  120  is registered, for example, by the client terminal T. That is, the client terminal T has a unit for registering in the relay server R information on the resources (resource information  126 ) which can be directly or indirectly operated by the client terminal T or information of the accounts of the different client terminals T sharing the resource. Accordingly, an operator can easily create and update the shared resource information  120  by the use of the display unit  605  of the client terminal T. 
     For example, the shared resource information  120  shown in  FIG. 36  is displayed on the display unit  605  of the client terminal  1 A and the like as shown in  FIG. 37 . The shared resource identification information  123 , the family account information  124 , and the family resource information  125  included in the shared resource information are simplified and displayed on the display unit. The operator can specify the client terminal T sharing the resource and can easily see the type or location of the shared resource, by viewing the display. By operating (clicking) the displayed resource, various processing operations such as copy can be performed in a picture for processing the resource. 
     In operating the resource, the relay server R can perform a seeming operation based on the update of the shared resource information  120  in one mode selected from two modes of a synchronous mode in which an essence of a resource is actually operated and an asynchronous mode in which the essence of the resource is not actually operated. 
     Here, the seeming operation based on the update of the shared resource information  120  is an operation of editing the details of the shared resource information  120  regardless of an essential operation of the resource, by operating the resource displayed on the display unit  605 . In other words, the operation of the resource is reflected at least in the shared resource information  120 . The information on the resources contained in the shared resource information  120  is displayed through a user interface as shown in  FIGS. 37 and 42 . By editing the shared resource information  120 , the user interface is also changed. Accordingly, a user is allowed to feel as if the essence of the resource is actually operated, whether the essence of the resource is operated. 
     One of both modes may be set in advance at the time of initially setting the relay communication system or may be selected by a user at the time of operating a resource. At the time of registering a resource as a shared resource, it may be established in advance in what mode the respective resources are operated. 
     The modes will be described with reference to the sequence diagrams of  FIGS. 38 to 40 .  FIGS. 38 to 40  show flows of the communication processes of performing a file copying operation and a file deleting operation, in which the modes are compared with each other. The relay group relation contained in the relay group information  100  of  FIG. 6  and the resource sharing relation contained in the shared resource information  120  of  FIG. 36  are set initially and the operations are performed under the set conditions. 
     Asynchronous Mode 
     In the first communication process, the client terminal  1 A of the LAN 1  copies an original file (file003.pdf) of which the owner is the client terminal  3 A disposed in the different LAN 3  into a folder (folderA) of itself to form a copy file (file003C.pdf). 
     The client terminal  1 A transmits a status changing request (UpdateResourceStatus command) for copying the original file (fiel003.pdf) to the relay server R 1  (step S 301 ). 
     When receiving the status changing request, the relay server R 1  determines whether the operation of copying the target resource can be processed by changing the details of the shared resource information  120 , on the basis of the shared resource information  120  (see  FIG. 36 ) stored in itself. When it is determined that the operation of copying the resource can be processed by changing the shared resource information  120 , the relay server updates the shared resource information  120 . 
     The updated shared resource information  120   j  is shown in  FIG. 41 . As shown in  FIG. 41 , the resource information  126   a  of a new copy file (file003C.pdf) is written in the family resource information  125  of the updated shared resource information  120   j . The owner information  128   a  (owner=‘user 3 A@account’) and the access information  129   a  (value=‘c:/folderB/file003.pdf’) are equal to the details of the resource information  126   t  as a copy source. The copy file is in a state where it is linked to the file of the copy source. That is, in the asynchronous mode, it is virtually shown that the copy operation has been performed by keeping the essence of the resource unchanged and changing the details of the shared resource information  120 . Accordingly, the essence of the resource is not changed with the copy operation and the repeated amount of resources occurring in the relay communication system decreases, thereby contributing to an efficient operation of the storage unit. 
     The relay server R 1  transmits the status changing request from the client terminal T registered therein to the client terminal T contained in the family account information  124  of the shared resource information  120  as a target. However, in this embodiment, since the corresponding client terminal T does not exist, the status changing request is not transmitted. 
     The change notification of the shared resource information  120  is transmitted to the relay servers R 2  and R 3  in which the different client terminals T ( 2 A and  3 A in this case) contained in the family account information  124  (steps S 301 . 1  and S 301 . 2 ). The relay servers R 2  and R 3  having received the change notification update the shared resource information  120  stored therein. The relay servers R 2  and R 3  transmit the status changing request to the client terminals  2 A and  3 A (steps S 301 . 1 . 1  and S 301 . 2 . 1 ). The client terminals having received the status changing request updates the shared resource information  120  stored therein and returns responses to the transmission sources, respectively. The responses are transmitted to the transmission sources, whereby a series of communication processes are ended. 
     The shared resource information displayed on the display unit  605  of the client terminal after the copy operation is shown in  FIG. 42 . The copy file (file003C.pdf) is formed under the folder (folderA) and it seems to perform the copy operation. 
     The next step shows the communication process in which the client terminal  2 A indirectly deletes a file (for example, file003C.pdf). 
     The client terminal  2 A transmits the status changing request for deleting file003C.pdf to the relay server R 2  (step S 302 ). 
     When receiving the status changing request, the relay server R 2  determines whether the operation of deleting a resource as a target can be processed by changing the details of the shared resource information  120 j, on the basis of the shared resource information  120   j  (see  FIG. 41 ) stored therein. The relay server R 2  determines that the deletion operation can be processed by changing the details of the shared resource information  120   j  and updates the shared resource information  120   j  stored therein. The status changing request is transmitted to a relevant client terminal T if any and the change notification of the shared resource information  120   j  is transmitted to the relevant relay servers R (R 1  and R 3  in this case) (steps S 302 . 1  and S 302 . 2 ). The relay servers R 1  and R 3  having received the change notification updates the shared resource information  120   j  stored therein and transmits the status changing request to the client terminals  1 A and  3 A (steps S 302 . 1 . 1  and S 302 . 2 . 1 ). The client terminals  1 A and  3 A having received the status changing request updates the shared resource information  120   j  stored therein and returns a response to the transmission source. The relay servers R 1  and R 3  having received the response transmit a response to the relay server R 2  as the transmission source, whereby a series of communication processes are ended. 
     Here, the details of the shared resource information  120   k  updated in the deletion operation are shown in  FIG. 43 . As shown in  FIG. 43 , the resource information  126   a  of the file (file003C.pdf) is deleted from the family resource information  125  of the updated shared resource information  120   k . The details of the shared resource information  120  displayed on the display unit  605  of the client terminal T after the deletion operation are the same as being shown in  FIG. 37  and it seems to actually operate the resource, whereby a user can user the client terminal without any particular consciousness. 
     In this way, in the asynchronous mode, by keeping the essence of the resource unchanged and changing only the details of the resource information  120 , the seeming operation of the resource is performed. 
     The operation of the resource may not be performed by only changing the details of the shared resource information  120 . For example, the client terminal  1 A copies the original file (file003.pdf), the owner of which is the client terminal  3 A, not to a folder included in the family resource information  125 , but to a local folder which is not a shared resource. Accordingly, in this case, the same process as the synchronous mode described below is performed in the asynchronous mode. 
     Synchronous Mode 
     First, the file copy operation is performed similarly to the asynchronous mode. The client terminal  1 A transmits a copy request (Copyfile) to the relay server R 1  (step S 303 ). The relay server R 1  having received the copy request specifies the owner client terminal  3 A of “file003.pdf” as a copy target on the basis of the shared resource information  120  and specifies the relay server R 3  in which the owner client terminal  3 A is registered on the basis of the relay group information  100 . 
     The relay server R 1  transmits an access request (INVITE) to the specified relay server R 3  through the external server S (step S 303 . 1 ). The relay server R 3  having received the access request transmits the copy request to the client terminal  3 A (step S 303 . 1 . 1 ). The client terminal  3 A having received the copy request transmits a response to the relay server R 3  and the relay server R 3  transmits the response to the relay server R 1 . 
     The relay server R 1  having received the response transmits a Mediasession command to the relay server R 3  (step S 303 . 2 ). The relay server R 3  having received the Mediasession command transmits the file copying request (GetFileData) to the client terminal  3 A (step S 303 . 2 . 1 ). The client terminal  3 A having received the file copying request copies “file003.pdf”, which can be directly operated by itself, from the resource storing unit  603  and transmits the copied file to the relay server R 3 . Then, “file003.pdf” is transmitted to the client terminal  1 A through the relay server R 1  (FileTransfer). 
     When a series of communication processes are finished, a cutting request (BYE) is transmitted from the relay server R 1  to the relay server R 3  and thus the communication between the relay server R 1  and the relay server R 3  is ended (step S 304 ). 
     Thereafter, in the client terminal  1 A, “file003.pdf” transmitted from the client terminal  3 A is stored as “file003C.pdf” in the folder (folderA) to form a new copy file (file003C.pdf). 
     The details of the shared resource information  120  are changed. First, the status changing request (UpdateResourceStatus) is transmitted from the client terminal  1 A having requested for the operation to the relay server R 1  (step S 305 ). The relay server R 1  having received the status changing request transmits a change notification (NOTIFY) of the shared resource information  120  to the relay servers R 2  and R 3  associated with the updated shared resource information  120  (step S 305 . 1  and S 305 . 2 ). The relay servers R 2  and R 3  having received the change notification update the shared resource information  120  stored therein. The status changing request is transmitted to the client terminals  2 A and  3 A associated with the updated shared resource information  120  (steps S 305 . 1 . 1  and S 305 . 2 . 1 ). The client terminals  2 A and  3 A having received the status changing request update the shared resource information  120  stored therein and transmit a response to the relay servers R 2  and R 3  as the transmission source. Thereafter, the response is transmitted from the relay servers R 2  and R 3  to the relay server as the transmission source and is transmitted from the relay server R 1  to the client terminal  1 A. 
     The shared resource information  120  is kept with the same details between the relevant relay servers R, even when it is updated. 
     The updated shared resource information  120   m  in the series of communication processes is shown in  FIG. 44 . As shown in  FIG. 44 , the resource information  126   c  of the copy file (file003C.pdf) is newly written in the family resource information  125  of the updated shared resource information  120   m . In the synchronous mode, since the essential operation of the resource is performed, information (owner=‘user1A@account’) indicating a new owner client terminal  1 A as the copy destination of the file is written in the owner information  128   c . Information (value=‘c:/folderA/file003C.pdf’) indicating a location of the file copied and newly created is written in the access information  129   c . That is, a copy file having the same details is actually newly created independently of the file of the copy source. 
     Up to now, since the client terminal  1 A was a user client terminal with respect to the original file (file003.pdf) as a copy source, the client terminal  1 A could not help operating the file indirectly through the client terminal  3 A. However, since the client terminal  1 A is the owner of the newly created copy file having the same details, the client terminal  1 A can operate the file directly. Accordingly, it is not necessary to operate the original file indirectly through the relay communication using the relay server R and it is thus possible to reduce a communication load as much. 
     After a series of processes of copying a file are performed in the synchronous mode, the details of the shared resource information  120  displayed on the display unit  605  of the client terminal T are the same as the details after the copy operation is performed in the asynchronous mode and thus they are not seemingly different from each other (see  FIG. 42 ). 
     A communication process in which a file (for example, file003C.pdf) is deleted in the synchronous mode is described now. 
     The client terminal  2 A transmits a deletion request (Deletefile) for deleting a file (file003C.pdf) to the relay server R 3  (step S 306 ). The relay server R 2  having received the deletion request specifies the owner client terminal  1 A of “file003C.pdf” as a deletion target and the relay server R 1  in which the owner client terminal  1 A is registered, on the basis of the shared resource information  120  and the relay group information  100 . 
     The relay server R 2  transmits an information notification of the deletion request (NOTIFY) to the specified relay server R 1  (step S 306 . 1 ). The relay server R 1  having received the information notification of the deletion request transmits the deletion request to the client terminal  1 A by the use of a Deletefile command (step S 306 . 1 . 1 ). The client terminal  1 A having received the deletion request deletes the target resource (file003C.pdf) from the resource storing unit  603 . The OK response is transmitted to the client terminal  2 A through the relay server R 1  and the relay server R 2 . 
     Subsequently, a process of updating the shared resource information  120   m  is performed between the relevant relay servers R. This is because the details of the shared resource information  120   m  are changed. Specifically, the status changing request is transmitted from the client terminal  2 A having requested for the operation to the relay server R 2  (step S 307 ). The relay server R 2  having received the status changing request transmits the change notification of the shared resource information  120  to the relay servers R 1  and R 3  associated with the changed shared resource information  120   m  (step S 307 . 1  and S 307 . 2 ). The relay servers R 1  and R 3  having received the change notification update the shared resource information  120   m  stored therein. The status changing request is transmitted to the client terminals  1 A and  3 A associated with the changed shared resource information  120   m  (steps S 307 . 1 . 1  and S 307 . 2 . 1 ). The client terminals  1 A and  3 A having received the status changing request update the shared resource information  120   m  stored therein and returns a response to the relay servers R 1  and R 3  as the transmission source. Thereafter, the response is transmitted from the relay servers R 1  and R 3  to the relay server R 2  as the transmission source and is then transmitted from the relay server R 2  to the client terminal  2 A. 
     In this way, the details of the shared resource information  120  after a series of processes of deleting a file is finished in the synchronous mode are equal to the details of the shared resource information  120  after the file deleting process is finished in the asynchronous mode (see  FIG. 43 ). Then, the details of the shared resource information  120  displayed on the display unit  605  of the client terminal T are equal to the details after the file is deleted in the asynchronous mode and thus no change occurs seemingly (see  FIG. 37 ). Accordingly, a user operating a resource by the use of the client terminal T can operate the resource without being aware of a difference between both modes, thereby not causing any confusion. 
     As described above, in the relay communication system employing the relay server according to the invention, a client terminal T can easily operate a resource held by a different client terminal T over the WAN, as if it holds the resource. 
     In addition, it is possible to select one of both modes of the synchronous mode and the asynchronous mode at the time of operating the resource. For example, when the synchronous mode is selected in which the status of the resource is contained in the operation details, the client terminal T having created a copy file after the operation can directly operate the copy file. As a result, the subsequent file operation cannot be necessary performed by the use of the owner client terminal T, thereby reduce a communication process load. On the other hand, when the asynchronous mode is selected, it is possible to prevent a resource from repeatedly occurring, thereby efficiently using the storage unit of the relay communication system. 
     While the invention has been described with reference to the preferred embodiments thereof, it will apparent to those skilled in the art that the disclosed invention may be modified in numerous ways and may assume many embodiments other than those specifically set out and described above. Accordingly, it is intended by the appended claims to cover all modifications of the invention that fall within the true spirit and scope of the invention.