referring now to fig1 to fig1 a and 10b , one embodiment of a mobile communication system according to the present invention will be described in detail . fig1 shows an exemplary configuration of a communication system according to this embodiment . in fig1 , a region enclosed by a dashed line 12 corresponds to a mobile carrier network portion , while a region enclosed by a chain line 11 corresponds to a home network portion . in the following , the exemplary case where a mobile terminal device 20 moves into the home network 11 while carrying out communications through the mobile carrier network 12 will be mainly described . in the mobile carrier network 12 , a plurality of network links are connected through a cellular phone network 6 and router devices 4 . each router device 4 has at least functions of an ordinary router compatible with the ipv6 . the mobile carrier network 12 is assumed to be originally providing the ordinary voice communication service , but a configuration for providing the ordinary voice communication service is omitted in fig1 . note that this embodiment is directed to the exemplary case where one mobile carrier manages its own packet communication network as a single management domain , but there can also be cases where one mobile carrier has a plurality of management domains , cases where a plurality of mobile carriers have a single common management domain , and any combination of these cases . the mobile terminal device 20 ( such as a portable terminal or a cellular phone , for example ) will be connected to the corresponding network link through a wireless base station 5 corresponding to a geographic location of the mobile terminal device 20 . then , the mobile terminal device 20 becomes capable of carrying out packet communications according to the ipv6 with a node located within the same network link , a node within the same management domain through the router device 4 , or a node ( such as a server 8 , for example ) located outside the management domain through the router device 4 and the internet 7 . on the other hand , in the home network 11 , various types of devices 2 and a gateway 1 are connected through a home local network 3 . the mobile terminal device 20 has a function for accessing this home local network 3 . also , the gateway device 1 is assumed to be connected to the external internet 7 through a fixed communication network 9 ( which is assumed to be an isp network here ). note that this embodiment is directed to the exemplary case where one internet service provider manages its own range for providing the internet connection service as a single management domain , but there can also be cases where one service provider has a plurality of management domains , cases where a plurality of service providers have a single common management domain , and any combinations of these cases . the mobile terminal device 20 and the devices 2 connected to the home local network 3 are capable of carrying out packet communications according to the ipv6 with the server 8 on the internet 7 through the gateway device 1 and the isp network 9 . in addition , they are also capable of carrying out packet communications according to the ipv6 with a server 10 for providing services limited only to members within the isp network 9 , for example , when such a server 10 exists . in this embodiment , the home local network 3 is assumed to be a local wireless network such as bluetooth , for example . note that , in fig1 , the dashed line 12 and the chain line 11 are depicted only for the sake of explaining the basic configuration logically , and they do not indicate an area covered by the wireless network . in this embodiment mobile terminal device 20 is assumed to be capable of accessing both the mobile carrier network 12 and the home local network 3 simultaneously . fig2 shows an exemplary configuration of the gateway device 1 in this embodiment . as shown in fig2 , this gateway device 1 comprises a first communication interface 31 for accessing the isp network 9 , a second communication interface 32 for accessing the home local network 3 , a data relay unit 33 for relaying between the first and second communication interfaces 31 and 32 , a service database 34 , a service lookup function unit 35 , and a network monitoring unit 36 . if necessary , the data relay device 33 may include a function for carrying out a protocol conversion , a media conversion , etc ., at a time of relaying between the first and second communication interfaces 31 and 32 . the service lookup function unit 35 is operated when a service lookup inquiry message is received through the the second communication interface 32 , to look up the requested service through the service database 34 or inquire the requested service to another server and returns the lookup result to the inquiring source . the network monitoring unit 36 is operated when a network state inquiry message is received through the second communication interface 32 , to returns a message containing information on a network state of the isp network 9 side to the inquiring source . note that the gateway device 1 may also have functions as the ipv6 compatible router in the home local network 3 , or another ipv6 compatible router may be provided in the home local network 3 . fig3 shows an exemplary configuration of the mobile terminal device 20 in this embodiment . as shown in fig3 , this mobile terminal device 20 comprises a first communication interface 24 for accessing the mobile carrier network 12 , a second communication interface 25 for accessing the home local network 3 , a voice communication unit 21 for carrying out ordinary voice communications , a packet communication unit 22 for carrying out packet communications according to the ipv6 , an address register 23 , an application list 26 , and an active register 27 . the mobile terminal device 20 is capable of relating a plurality of ipv6 addresses with respect to the same communication interface ( capable of sending packets by using a plurality of ipv6 addresses from the same communication interface ). the address register 23 is used for the purpose of storing these addresses . a various ipv6 applications are to be operated on the mobile terminal device 20 side , and an application list 26 is used for storing a list of these applications ( which includes information for identifying each application ( a file name , for example ) and an application type of each application , for example ). also , when the specific application is activated by the user , the active register 27 registers information regarding the currently operated application ( such as information for identifying that application , application type of that application , and information for indicating a communication interface used for that application ( either the first communication interface or the second communication interface ), for example ). here , the address scope defined in the ipv6 will be described ( see rfc 2373 for further details ). this is an address valid only within the same network link , which has a prefix of 1111 1110 10 in the ipv6 . this is an address valid only within the same management domain , which has a prefix of 1111 1110 11 in the ipv6 . in the example of fig1 , the mobile terminal device 20 connected to the mobile carrier network 12 can carry out communications using ( arbitrary address containing ) the link local address with respect to the server 4 ( which is in a positional relationship of being located ) on the same network link as the mobile terminal device 20 , and communications using a site local address ( or a global address ) with respect to a server ( which is in a positional relationship of being located ) in the same management domain as the mobile terminal device 20 . on the other hand , the mobile terminal device 20 connected to the mobile carrier network 12 will carry out communications using a global address with respect to the server 8 ( which is in a positional relationship of being located ) on the general internet 7 . now , the first communication interface 24 of this mobile terminal device 20 can be always assigned with one or both of the link local address and the site local address . the link local address and the site local address will be derived from the prefix defined in the ipv6 and the device id of this mobile terminal device 20 . note that it is also possible for the communication service provider to assign arbitrary address as an address to be used in the same network link . also , which one of the link local address alone , the site local address alone , and both the link local address and the site local address is to be always assigned can be determined according to the policy of the communication service provider . by always assigning the link local address alone , the site local address alone , or both the link local address and the site local address , the mobile terminal device 20 becomes always capable of utilizing ( carrying out communications for ) on - link services using ( arbitrary address containing ) the link local address ( such as the advertisement delivery from a specific wireless base station group , for example ), and / or services within domain which are services of the service provider in this embodiment ( such as information service limited to the users of that service provider , for example ). on the other hand , the global address to be assigned will be generated from a network prefix delivered from the nearest neighbor router device 4 and the id information ( eui - 64 ) of the mobile terminal device 20 , according to the “ stateless address autoconfiguration ” ( rfc 2461 ) defined in the ipv6 . the basic procedure for the global address generation is as follows . namely , the router device 4 regularly broadcasts a router advertisement message on - link , or the router device 4 returns a response message upon receiving an inquiry message , and the mobile terminal device 20 receives the router advertisement message , or sends an inquiry message and receives the response message , generates the global address by using the network prefix contained in the received message , and transmits an address information notification message containing the generated ipv6 address and a mac address to the router device 4 side . upon receiving the address information notification message , the router device 4 makes an entry of a corresponding information into a corresponding table called neighborhood cache ( which corresponds to the arp table in the ipv4 ). as a result , the nearest neighbor router device 4 will carry out the delivery of packets destined to the mobile terminal device 20 . note that the user may be allowed to freely carry out the acquisition , setting and starting of the use of the ipv6 global address , or the discarding , setting and ending of the use of the ipv6 global address . alternatively , it is also possible to use a provision in which the processing for starting the use of the global address is carried out when the user of the mobile terminal device 20 activates an application that requires the global address , and the processing for ending the use of that global address is carried out when that application is finished . in this embodiment , the assignment of the global address to the second communication interface 25 of the mobile terminal device 20 is to be controlled using the above described address scope function . in the example of fig1 , when the same network link is set to be within the home network 11 , the mobile terminal device 20 connected to the home network 11 can carry out communications using ( arbitrary address containing ) the link local address with respect to a correspondent such as the other device 2 or the gateway device 1 through the home local network 3 , and when the same site is set to be within the isp network 9 , the mobile terminal device 20 connected to the home network 11 can carry out communications using a site local address ( or a global address ) with respect to a correspondent such as the server 10 within the isp network 9 . on the other hand , the mobile terminal device 20 connected to the isp network 9 via the home network 11 will carry out communications using a global address with respect to the server 8 on the general internet 7 . in the following , the operation in the case where the mobile terminal device 20 moves toward the home network 11 while receiving the service on the mobile carrier network 12 side by using the assigned global address , and establishes a wireless link with the home local network 3 to become a member of the home network 11 , will be described . fig4 shows an exemplary processing procedure of the mobile terminal device 20 in this case . first , the global address is assigned to the mobile terminal device 20 at the mobile carrier network 12 side ( step s 11 ), and when the mobile terminal device 20 approaches to the home network 11 while receiving the service on the mobile carrier network 12 side , the mobile terminal device 20 detects radio signals of the other devices and establishes a link ( step s 12 ). this wireless link establishing can be realized by a method specified for each radio medium . at this point , if there is no particular job that uses the local network on the bluetooth side , it suffices to wait in the wireless link established state . next , suppose that a service on the bluetooth link side is requested from the mobile terminal device 20 . this request can be made by a task unique to the mobile terminal device 20 , or by sending a result of a task on the mobile carrier network 12 side to some device on the bluetooth network side by utilizing a direct bridging , for example . at this point , the mobile terminal device 20 looks up a resource ( a desired service ) to be accessed on the bluetooth side ( step s 13 ). in this case , it is possible to use various methods such as a method using sdp ( service discovery protocol ) defined in the bluetooth , a method using slp ( service location protocol ) for looking up arbitrary service on the internet , etc ., and any suitable combination can be used according to factors such as a range to be looked up , a type of a service to be looked up , etc . here , it is assumed that the resource on the local bluetooth link will be looked up by using the sdp first , and if it cannot be found , the wider range will be looked up by using the slp . it is also possible to use a configuration in which the gateway device 1 of fig2 relays a query message for that purpose and becomes an agent of the slp itself , for example . next , the mobile terminal device 20 acquires a necessary address ( a link local address , a site local address or a global address ) according to a positional relationship between the mobile terminal device 20 and the correspondent as obtained from the service lookup result , and assigns it to the second communication interface 25 ( step s 14 ). then , the mobile terminal device 20 utilizes the desired service ( step s 15 ). thereafter , the steps s 13 to s 15 will be repeated according to the need . however , the step s 14 can be skipped when the necessary address is already acquired . next , the above described service lookup result will be described for three different cases . first , in the case where the resource is found to be a link locally accessible one in the home local network 3 as a result of the service lookup , the communications will be carried out by assigning the link local ipv6 address to the home local network 3 side in the mobile terminal device 20 . this procedure will be used in the case of storing the image data downloaded from the mobile carrier network 12 side into a disk for a pc as shown in fig5 , for example . next , in the case where the resource is found to be a site locally accessible one in the isp network 9 on the home local network 3 side as a result of the service lookup , the communications will be carried out by assigning the site local ipv6 address to the home local network 3 side in the mobile terminal device 20 . this procedure will be used in the case of receiving the service limited only to members of the isp which is provided by the server 10 in the isp network 9 as shown in fig6 , for example . on the other hand , in the case where the resource is found to be located on the global internet 7 as a result of the service lookup , the communications will be carried out by assigning a global ipv6 address to the home local network 3 side in the mobile terminal device 20 . at this point , the mobile terminal device 20 becomes capable of accessing the resource located on the global internet 7 either via the mobile carrier network 12 , or via the gateway device 1 through the home local network 3 . this is the state called “ multi - home ” in which the mobile terminal device 20 becomes a router having two communication interfaces which are connected to different providers . in the case of this multi - home state , both of the communication interfaces can be made available . in such a case , one communication interface can be used mainly while the other communication interface is used as a back - up , and which communication interface should be used mainly can be determined according to factors such as the congestion state of each network , the charging state of each network , etc . for example , the home network 11 side can be selected when the charge is much cheaper on the isp network side ( the fixed network side ), or the mobile carrier network 12 side can be selected when the network speed is faster on the mobile carrier network 12 side . also , the communication interface to be selected can be determined by accounting for a dynamically varying state , instead of determining it fixedly . such a policy can be set by the user or a vendor of the terminal in advance into a control unit ( not shown ) inside the mobile terminal device 20 . note that the state or the like of the isp network 9 side may be acquired by inquiring it to the gateway device 1 or the like , for example . also , the mobile terminal device 20 itself may maintain the charging condition or the like of the isp network 9 side . similarly , the state or the like of the mobile carrier network 12 side may be acquired by inquiring it to a prescribed server device or the like on the mobile carrier network 12 side , for example . also , the mobile terminal device 20 itself may maintain the charging condition or the like of the mobile carrier network 12 side . fig7 shows an exemplary processing procedure of the mobile terminal device 20 in this case . namely , in the case where the global address is available on both the mobile carrier network 12 side and the home network 11 side ( step s 21 yes , step s 22 yes ), which one of the global address on the mobile carrier network 12 side and the global address on the home network 11 side should be used is determined according to various factors ( step s 23 ). now , while the processing on the home local network 3 side in the mobile terminal device 20 is carried out in this way , the job on the mobile carrier network 12 side may be finished . this job status on the mobile carrier network 12 side regarding the finished state can be detected by regularly checking the active register 27 in the mobile terminal device 20 . when all the jobs on the mobile carrier network 12 side are finished , the entire network setting on the mobile carrier network 12 side is released , such that the necessary setting is concentrated into that on the home local network 3 side . this measure is taken from a viewpoint of not wasting the access channel resources unnecessarily . fig8 shows an exemplary processing procedure of the mobile terminal device 20 in this case . namely , when all the jobs on the mobile carrier network 12 side are finished ( step s 31 yes ), the entire network setting on the mobile carrier network 12 side is released ( step s 32 ). note that it is also possible to use a provision in which the mobile terminal device 20 transmits a message for notifying the finishing of all the services received via the mobile carrier network 12 to the gateway device 1 through the home local network 3 , and the gateway device 1 notifies a message for setting up a global address ( via the isp network 9 ) to be set up on the home local network 3 side to the mobile terminal device 20 upon receiving the above message from the mobile terminal device 20 if such a global address is not set up yet . now , it is also possible to use a provision in which the network setting on the mobile carrier network 12 side is not released but reserved as an emergency communication path for the device 2 on the home local network 3 side to access the internet 7 at a time of fault in the gateway device 1 or the isp network 9 , for example . even in this case , all the existing devices 2 are initialized by the network setting on the home local network 3 side , so that they cannot use the channel of the mobile terminal device 20 without a further change , and for this reason , there is a need for the mobile terminal device 20 to function as a gateway with respect to the devices 2 on the home local network 3 side by carrying out the nat / proxy processing , etc . fig9 shows an exemplary processing procedure of the mobile terminal device 20 in this case . namely , when the mobile terminal device 20 is going to be a gateway of the home network side ( step s 41 yes ), the nat / proxy processing , etc ., are carried out ( step s 42 ). also , in practice , the mobile terminal device 20 establishes the network setting on the home local network 3 side gradually , so that it is possible to make a transition to the state of using a link on the home local network 3 side regardless of the communication interface on the mobile carrier network 12 side . also , in the above , it is assumed that the communication interface to be used for the application is not to be changed during the communications for that application , but it is also possible to change the communication interface at appropriate timing during the communications for that application ( from the mobile carrier network 12 side to the home local network 3 side , for example ). note that , for the job that requires the link local or site local resource access on the mobile carrier network 12 side , the communication interface on the mobile carrier network 12 side is to be used until this job is finished ( or until this job is cancelled ). now , using the specification of the mobile ipv6 which is currently under the standardization process by the ietf , it is possible to guarantee the mobility by regarding the mobile terminal device 20 that is actually connected to the mobile carrier network 12 side as having moved to the home local network 3 side . here , a method for switching the belonging network according to the mobile ipv6 will be described with references to fig1 a and 10b . fig1 a shows an exemplary packet header in this case , which contains a source address ( cn ), a destination address ( addr 1 ) and a destination option ( via addr 2 ). here , cn is a global address of the correspondent , addr 1 is a global address of the mobile terminal device 20 on the mobile carrier network 12 side , and addr 2 is a global address of the mobile terminal device 20 on the home local network 3 side . also , the destination option specifies a location through which the packet should be transferred . using the destination option of the ipv6 , as shown in fig1 b , a packet transmitted from a correspondent 30 will be controlled to be transferred to the original address on the mobile carrier network 12 side via the address on the home local network 3 side . then , in practice , the fact that this packet is destined to the mobile terminal device 20 is ascertained when the packet is captured at the address on the mobile carrier network 12 side , and the packet communication using a direct route becomes possible as the mobile terminal device 20 acquires this packet . in the above , the case where the mobile terminal device 20 moves from the mobile carrier network 12 side into the home local network 3 side has been described , but the reverse case where the mobile terminal device 20 moves from the home local network 3 side out to the mobile carrier network 12 side can also be controlled similarly . namely , the mobile terminal device 20 can establish a wireless link with the mobile carrier network 12 side , assign the necessary ipv6 addresses according to the address scopes of the necessary resources , and concentrates the setting to that of the mobile carrier network 12 side by releasing the address setting on the home local network 3 side when the jobs on the home local network 3 side are eventually finished . also , the route selection policy in the case of becoming the multi - home state in a course of this operation can be determined similarly . also , in the above , it is assumed that the mobile terminal device 20 has the ordinary voice communication function , but the mobile terminal device 20 may have communication functions for information in other forms such as text communications in addition to or instead of the ordinary voice communication function . the mobile terminal device 20 may be a device which is capable of utilizing only the internet service . the similar modifications are also possible with respect to the services provided by the communication service provider . as described , according to the present invention , in the case where the mobile terminal device moves into the home local network while carrying out communications in the mobile carrier network , it is possible to construct the home local network side setting in the mobile terminal device phase by phase , according to the resources that become necessary in the home local network . also , in the case where the mobile terminal device temporarily becomes the so called multi - home state in which the ipv6 global addresses are assigned to both the home local network and the mobile carrier network , which one of the two communication interfaces should be used mainly can be determined appropriately by accounting for the user &# 39 ; s preference regarding the network state , the charging condition , etc . in addition , in the case where the communication jobs on the mobile carrier network side are finished , the mobile terminal device can release the network setting immediately such that all communications can be concentrated to those via the home local network . furthermore , these setting conditions can be finely adjusted according to the user &# 39 ; s preference , such that it is possible to freely devise a policy ( within a range of violating the scope rule for each application , for example ) such as that all the jobs are re - constructed as the home local network based ones immediately once the wireless link with the home local network is established , as long as no service dependent on the mobile carrier network side is received , for example . thus according to the present invention , the mobile terminal device can judge whether the resource necessary on the local network side is a resource that is on - link ( a device with which communications can be carried out directly ), or a resource that is closed within the same site , or a resource other than these , by using the service lookup or the like , and assign the ipv6 address of the scope corresponding to that location to the local network side . when the required resource is on the global internet , it is accessible from both the mobile communication network and the fixed network , and it is possible to judge whether the mobile terminal device is to become a router in the multi - home state or the access is to be continued on the mobile communication network side alone , for example , by accounting for the network state , the charging condition , etc . it is also possible to update the network setting such that the internet service can be continued by the fixed communication network side alone by releasing the address on the mobile communication network side , when all the services of the mobile communication network are finished as the time elapses , for example . it is also possible to carry out the similar control even in the case of making a transition from the fixed communication network to the mobile communication network in the reverse direction . consequently , according to the present invention , in the case where the mobile terminal device moves into the local network while receiving the communication services on the mobile communication network side , it is possible to determine the address setting , the communication route selection , etc ., on the local network side appropriately by accounting for the user &# 39 ; s policy , the necessary resources , etc . note that the home network used in the above described can be replaced by any other local network without affecting the applicability of the present invention . note also that , in the present invention , the existing ipv6 devices can be used without requiring any modification , and the conventional ipv6 addressing architecture can be used without any change . consequently , it is advantageous in terms of the compatibility with the existing devices . note also that the present invention can be easily expanded according to the network management policies of the various mobile carriers . the present invention is also applicable not only to the ipv6 but also to the packet communications using the cellular phones that are proposed recently . it is to be noted that the above described embodiments according to the present invention may be conveniently implemented using a conventional general purpose digital computer programmed according to the teachings of the present specification , as will be apparent to those skilled in the computer art . appropriate software coding can readily be prepared by skilled programmers based on the teachings of the present disclosure , as will be apparent to those skilled in the software art . in particular , each of the gateway device and the mobile terminal device of the above described embodiment can be conveniently implemented in a form of a software package . such a software package can be a computer program product which employs a storage medium including stored computer code which is used to program a computer to perform the disclosed function and process of the present invention . the storage medium may include , but is not limited to , any type of conventional floppy disks , optical disks , cd - roms , magneto - optical disks , roms , rams , eproms , eeproms , magnetic or optical cards , or any other suitable media for storing electronic instructions . it is also to be noted that , besides those already mentioned above , many modifications and variations of the above embodiments may be made without departing from the novel and advantageous features of the present invention . accordingly , all such modifications and variations are intended to be included within the scope of the appended claims .