Abstract:
A low cost communication apparatus enables detection of an apparatus present on a different network in a router multistage network having a plurality of routers. When a communication apparatus cannot detect, on a network thereof, a desired apparatus, the communication apparatus requests a connection support server securing communication paths with all the apparatuses on a home network, to relay an apparatus detection request. The connection support server transfers the request to relay the apparatus detection request, to an arbitrary apparatus belonging to a different network from the network to which the communication apparatus belongs, and the arbitrary apparatus, by proxy, performs an apparatus detection, and transfers information about a detected apparatus to the connection support server. By obtaining the information from the connection support server, the communication apparatus detects the apparatus on the different network.

Description:
TECHNICAL FIELD 
     The present invention relates to a connection support server and a communication apparatus, and relates to a connection support server and a communication apparatus which enable detection of an apparatus present on a different network in a network comprising a plurality of routers. 
     BACKGROUND ART 
     While always-on Internet connections are widespread and various services have appeared accordingly, there is a demand to be able to receive such services in various places at home. Generally speaking, each home has a different home network configuration, and apparatuses used therein are various such as PCs, Internet appliances and the like. However, there is problem that connection settings or connection operations of Internet appliances are difficult for general users who do not have technical knowledge of such a network, and it is also difficult to establish a connection between apparatuses if a configuration of the network, such as a connection mode, router type or the like, is not taken into account. 
     In order to solve this problem, there is a technique called UPnP (Universal Plug and Play) stipulated by the UPnP Forum, which allows apparatuses within a home network to be interconnected. 
     By using UPnP, an apparatus within a home network can be automatically searched for and detected by multicasting, and an interconnection with the detected apparatus can be established. 
       FIG. 17A  shows a home network comprising conventional UPnP apparatuses. In  FIG. 17A , a modem having a router function, which is rented from an Internet service provider, is connected to a PC, a television and a VCR.  FIG. 17B  shows a process for detecting an apparatus by UPnP, which is performed in the case of operating the VCR from the PC. 
     In  FIG. 17B , the PC first multicasts, on the network, an apparatus detection request which contains information indicating that a search target is the VCR (step S 201 ). The apparatus detection request is received by all the UPnP apparatuses on the network, and each apparatus determines whether or not the search target is said each apparatus. 
     The VCR determines that the search target is the VCR, and transmits, to the PC which is a transmission source of the request, an apparatus detection response which contains necessary information for operating the VCR (step S 202 ). By receiving the apparatus detection response, the PC is enabled to operate the VCR. 
     Using UPnP in this manner enables UPnP apparatuses to be interconnected. 
     In recent years, however, it has become common that a user connects a router having a wireless function, which the user has purchased, to a modem which functions as a router and which is rented from an Internet service provider, such that each router has apparatuses subordinately connected thereto as shown in  FIG. 18A  (hereinafter, this type of network configuration will be referred to as a router multistage configuration).  FIG. 18B  shows a process for detecting an apparatus by UPnP, which is performed when it is desired in  FIG. 18A  to control a VCR from a PC. 
     As shown in  FIG. 18B , the PC first multicasts, on a network thereof, an apparatus detection request which contains information indicating that a search target is the VCR (step S 301 ). The apparatus detection request is received by all the UPnP apparatuses on the network (a wireless router and a television T 2  in  FIG. 18A ), and each apparatus determines whether or not said each apparatus is the search target. 
     Here, a general commercially available household router is configured, in consideration of security, so as not to transfer a multicast packet to another network. For this reason, in the router multistage configuration as shown in  FIG. 18A , the wireless router does not transfer, to a private network N 1 , an apparatus detection request packet received from the PC. Therefore, the VCR which is the search target cannot receive the apparatus detection request, and does not return an apparatus detection response. Accordingly, an apparatus detection response reception waiting time-out occurs in the PC (step S 302 ), and thus the apparatus detection fails (step S 303 ). 
     As described above, in the router multistage configuration, an apparatus on the same network can be detected using UPnP multicasting. However, an apparatus on a different network cannot be detected. 
     Conventionally, there are a disclosed network connection apparatus and method (e.g., Patent Document 1) in which a plurality of networks, each of which is independently configured, are connected such that a plurality of devices on the respective networks can be interconnected. 
     According to the network connection apparatus and method of Patent Document 1, the plurality of networks, each of which is independently configured, are respectively provided with network connection apparatuses, and each network connection apparatus manages information about apparatuses on a corresponding network. The network connection apparatuses exchange such information each other, and this enables apparatuses on different networks to be interconnected. 
       FIG. 19A  shows a router multistage home network in which gateways each including the network connection apparatus of Patent Document 1 are provided. It is assumed here that a network connection apparatus D 1  has already obtained, as access information about a network connection apparatus D 2 , an IP address and a port number of a gateway G 2 , and the network connection apparatus D 2  has already obtained, as access information about the network connection apparatus D 1 , an IP address and a port number of a gateway G 1 .  FIG. 19B  shows a process for detecting an apparatus by using the network connection apparatus and method of Patent Document 1, which process is performed in the case of operating a VCR from a PC in  FIG. 19A . 
     As shown in  FIG. 19B , the network connection apparatus D 1  collects, by multicasting an apparatus detection request, information about apparatuses (television T 1 , VCR) on a private network N 1  (step S 401 ). Similarly, the network connection apparatus D 2  collects, by multicasting an apparatus detection request, information about apparatuses (PC, television T 2 ) on a private network N 2  (step S 402 ). 
     Next, the PC on the private network N 2  transmits, to the network connection apparatus D 2 , an apparatus detection request which contains information indicating that a search target is the VCR (step S 403 ). Upon receiving the request, the network connection apparatus D 2  sets an IP address and a port number of the gateway G 1  as a transmission destination, and then transfers the apparatus detection request to the network connection apparatus D 1  (step S 404 ). The network connection apparatus D 1  searches the apparatus information obtained at step S 401  for information about the VCR which is the search target contained in the received apparatus detection request, and transmits the information about the VCR to the network connection apparatus D 2  as an apparatus detection response (step S 405 ). Upon receiving the apparatus detection response, the network connection apparatus D 2  transfers the response to the PC which is a transmission source of the request (step S 406 ). In the above manner, the PC is enabled to operate the VCR which is on a different network.
         [Patent Document 1] Japanese Laid-Open Patent Publication No. 2004-320741       

     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, the method disclosed in Patent Document 1 needs to meet requirements described below in order to realize an interconnection between apparatuses on different networks. 
     A first requirement is that networks divided by gateways are each required to have one network connection apparatus. 
     A second requirement is to input address information about each gateway to each network connection apparatus. 
     For example, in the case of a home network having a router multistage configuration, a same number of network connection apparatuses as a number of provided routers (i.e., as a number of networks divided by the routers) are necessary in order to meet the first requirement. This causes a problem that a cost for the user becomes a substantial amount. 
     Also, in order to meet the second requirement, it is necessary for the user to manually set, for all the network connection apparatuses, address information about all the routers, and thus the general user who does not have enough network knowledge is required to do difficult troublesome work. A conceivable manner to eliminate the necessity for the user to do such work is to mount, on each router, a network connection apparatus which has a mechanism for exchanging address information, or to provide routers each having a mechanism for exchanging router address information. However, replacing all the routers in the home network with dedicated routers still causes the problem that the cost for the user becomes a substantial amount. 
     Therefore, an object of the present invention is, in view of the above-described problem, to provide a communication apparatus which allows a network to be configured with a low cost and a simple process. 
     Solution to the Problems 
     The present invention is directed to a communication apparatus having a connection support server function, which is, in a network comprising a plurality of subnetworks connected via a plurality of NAT devices, connected to an arbitrary subnetwork in the network and which has an established communication path with a communication apparatus connected to a different subnetwork from the subnetwork to which the communication apparatus having the connection support server function is connected. In order to achieve the above object, the communication apparatus of the present invention comprises: a relay request transfer section for, when receiving from an arbitrary communication apparatus a relay request for an apparatus detection request, transferring to another communication apparatus the relay request for the apparatus detection request; and an apparatus detection response transfer section for, when receiving an apparatus detection response, transferring the received apparatus detection response to the communication apparatus which is a transmission source of the relay request. When receiving the relay request for the apparatus detection request, the relay request transfer section transfers the relay request for the apparatus detection request, to an arbitrary communication apparatus connected to a different subnetwork from a subnetwork to which the communication apparatus which is the transmission source of the relay request is connected. The apparatus detection response transfer section has the connection support server function for, when receiving the apparatus detection response from the communication apparatus to which the relay request for the apparatus detection request has been transferred, transferring the apparatus detection response to the communication apparatus which is a transmission source of the apparatus detection request. 
     This enables the communication apparatus, which is the transmission source of the apparatus detection request, to detect a communication apparatus present on a different subnetwork. 
     Preferably, the communication apparatus further comprises: an apparatus detection request transmission section for multicasting or broadcasting, on the subnetwork thereof, an apparatus detection request for a desired communication apparatus; a relay request transmission section for transmitting a relay request for the apparatus detection request, to the communication apparatus on the different subnetwork; and an apparatus detection response receiving section for receiving an apparatus detection response. The apparatus detection request transmission section transmits, on the subnetwork thereof, the apparatus detection request for the desired communication apparatus. In the case where the apparatus detection response receiving section does not receive the apparatus detection response to the apparatus detection request, the relay request transmission section transmits the relay request for the apparatus detection request, to the communication apparatus on the different subnetwork. The apparatus detection response receiving section receives the apparatus detection response to the relay request, thereby detecting the desired communication apparatus. 
     This enables the communication apparatus of the present invention to detect a desired communication apparatus within the network. 
     When receiving, from the communication apparatus on the different subnetwork, the relay request for the apparatus detection request, the relay request transfer section performs an apparatus detection on the subnetwork thereof, by multicasting or broadcasting the apparatus detection request, and transfers the relay request for the apparatus detection request, to an arbitrary communication apparatus on all other subnetworks. 
     This allows the communication apparatus of the present invention to omit steps in which the apparatus detection request is relayed, on the subnetwork of the communication apparatus, to an arbitrary communication apparatus and the arbitrary apparatus on the subnetwork performs multicasting or broadcasting. Accordingly, a time consumed for the search can be reduced. 
     When the relay request transfer section has received, on the subnetwork thereof, a multicasted or broadcasted apparatus detection request from a communication apparatus on the subnetwork, the relay request transfer section transmits a relay request for the apparatus detection request, to an arbitrary communication apparatus on the different subnetwork. 
     This enables the communication apparatus of the present invention to perform an apparatus detection on the different subnetwork at the same time as a communication apparatus, which is present on the subnetwork of the communication apparatus of the present invention and which has multicasted or broadcasted the apparatus detection request on the subnetwork, waits for a response to the apparatus detection request. Accordingly, a time to be consumed when an apparatus to detect is not present on the subnetwork, can be reduced. 
     The relay request transfer section stores information about communication apparatuses, and when receiving the relay request for the apparatus detection request, the relay request transfer section determines, based on the information about the communication apparatuses, a communication apparatus to which the relay request is to be transferred. 
     This enables the communication apparatus of the present invention to always cause only an apparatus having a high processing capability to multicast or broadcast the apparatus detection request, and thereby prevent a processing load from being imposed on a communication apparatus having a low processing capability. This also allows the communication apparatus of the present invention to always request a different communication apparatus to multicast or broadcast the apparatus detection request, in order for the processing to be performed in a dispersed manner. As a result, stability of the network can be obtained. 
     The communication apparatus further comprises a relay rejection response receiving section for receiving a rejection response to the relay request for the apparatus detection request. When receiving the rejection response, the relay rejection response receiving section transfers the relay request for the apparatus detection request, to a different communication apparatus from a communication apparatus which is a transmission source of the rejection response, the different communication apparatus existing on a same subnetwork as that of the communication apparatus which is the transmission source of the rejection response. 
     This allows the communication apparatus of the present invention to, in the case where a communication apparatus which is requested to relay the apparatus detection request is unable to multicast or broadcast the apparatus detection request due to a load imposed thereon, request another communication apparatus, on which a processing load is not imposed, to relay the apparatus detection request. This prevents the communication apparatus from becoming incapable of performing processing. 
     The present invention is also directed to a communication apparatus which is, in a network comprising a plurality of subnetworks connected via a plurality of NAT devices, connected to an arbitrary subnetwork in the network and which has an established communication path with a communication apparatus which has a communication path connected to a communication apparatus on the network and which has a connection support server function. In order to achieve the above object, the communication apparatus of the present invention comprises: an apparatus detection request transmission section for multicasting or broadcasting, on the subnetwork thereof, an apparatus detection request for a desired communication apparatus; a relay request transmission section for transmitting a relay request for the apparatus detection request, to the communication apparatus having the connection support server function; and an apparatus detection response receiving section for receiving an apparatus detection response. The apparatus detection response receiving section receives the apparatus detection response from the desired communication apparatus or from the communication apparatus having the connection support server function, thereby detecting the desired communication apparatus. 
     This allows the communication apparatus of the present invention to detect a communication apparatus on a different subnetwork. 
     In the case where the apparatus detection response receiving section does not receive the apparatus detection response to the apparatus detection request, the relay request transmission section transmits the relay request for the apparatus detection request, to the communication apparatus having the connection support server function. 
     This allows the communication apparatus of the present invention to, only when a desired communication apparatus is not present on the subnetwork of the communication apparatus of the present invention, perform the relay request for the apparatus detection request, whereby an unnecessary packet transmission on the network can be prevented. 
     At the same time as the apparatus detection request transmission section multicasts or broadcasts the apparatus detection request on the subnetwork thereof, the relay request transmission section transmits the relay request for the apparatus detection request, to the communication apparatus having the connection support server function. 
     This enables the communication apparatus of the present invention to, in the case where a desired communication apparatus is not present on the subnetwork of the communication apparatus of the present invention, perform an apparatus detection on a different subnetwork at the same time as waiting for a response reception. Accordingly, a time, which is consumed until the desired communication apparatus is detected, can be reduced. 
     The communication apparatus further comprises a relay request processing section for multicasting or broadcasting an apparatus detection request on the subnetwork thereof when receiving, from the communication apparatus having the connection support server function, a relay request for the apparatus detection request. When the apparatus detection response receiving section has received the apparatus detection response, the relay request processing section transfers the received apparatus detection response to the communication apparatus having the connection support server function. 
     This allows the communication apparatus of the present invention to perform detection of a communication apparatus on the subnetwork of the communication apparatus of the present invention, by proxy for a communication apparatus on another subnetwork, and transfer the response via the communication apparatus having the connection support server function. This enables the communication apparatus which is a transmission source of the relay request to detect the communication apparatus present on a different subnetwork. 
     The communication apparatus further comprises a relay rejection response transmission section for, when the relay request processing section has received, from the communication apparatus having the connection support server function, the relay request for the apparatus detection request and determined that a processing capability of the relay request processing section is insufficient for multicasting or broadcasting the apparatus detection request on the subnetwork thereof, transmitting, to the communication apparatus having the connection support server function, a rejection response to the relay request for the apparatus detection request. 
     This allows, in the case where the communication apparatus of the present invention is, when receiving the relay request for the apparatus detection request, unable to multicast or broadcast the apparatus detection request due to a processing load imposed thereon, the communication apparatus to reject the request. This prevents the communication apparatus from becoming incapable of performing processing. 
     The above-described series of processing sequences performed by the communication apparatuses may be implemented as methods to be executed by the communication apparatuses. Further, the present invention may be a storage medium for storing software in which the methods are implemented. 
     EFFECT OF THE INVENTION 
     The present invention enables detection of a desired communication apparatus whichever network the communication apparatus belongs to in a router multistage home network, and prevents misplacement of a communication apparatus even if a user does not have special knowledge. Further, routers to be used in the home network may be commercially available routers, and only one apparatus on the home network is required to have a connection support server function. Therefore, a cost for the user can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an exemplary configuration of an entire system according to a first embodiment of the present invention. 
         FIG. 2  is a block diagram showing an exemplary configuration of a connection support server  001  according to the first embodiment of the present invention. 
         FIG. 3A  is a block diagram showing an exemplary configuration of a communication apparatus  101  according to the first embodiment of the present invention. 
         FIG. 3B  is a block diagram showing an exemplary configuration of a communication apparatus  102  according to the first embodiment of the present invention. 
         FIG. 3C  is a block diagram showing an exemplary configuration of a communication apparatus  201  according to the first embodiment of the present invention. 
         FIG. 3D  is a block diagram showing an exemplary configuration of a communication apparatus  202  according to the first embodiment of the present invention. 
         FIG. 4  shows a processing sequence, of the first embodiment of the present invention, for detecting the communication apparatus  201  connected to a subordinate network from the communication apparatus  101  connected to a superordinate network. 
         FIG. 5  shows a processing sequence, of the first embodiment of the present invention, in which the connection support server  001  transmits, at the same time as the connection support server  001  receives an apparatus detection request from the communication apparatus  101  on a network of the server  001 , a relay request to an arbitrary communication apparatus on a different network. 
         FIG. 6  shows a processing sequence, of the first embodiment of the present invention, for detecting the communication apparatus  102  connected to a superordinate network from the communication apparatus  202  connected to a subordinate network. 
         FIG. 7  shows a processing sequence, of the first embodiment of the present invention, in which the connection support server  001  multicasts, on a network thereof, an apparatus detection request to communication apparatuses at the same time as the connection support server  001  receives a relay request for an apparatus detection request from the communication apparatus  202  on a different network. 
         FIG. 8  shows an exemplary configuration of an entire system according to a second embodiment of the present invention. 
         FIG. 9A  is a block diagram showing an exemplary configuration of a communication apparatus  301  according to the second embodiment of the present invention. 
         FIG. 9B  is a block diagram showing an exemplary configuration of a communication apparatus  302  according to the second embodiment of the present invention. 
         FIG. 10  shows a processing sequence, of the second embodiment of the present invention, for detecting the communication apparatus  201  connected to a subordinate network from the communication apparatus  101  connected to a superordinate network. 
         FIG. 11  shows a processing sequence, of the second embodiment of the present invention, for detecting the communication apparatus  102  connected to a superordinate network from the communication apparatus  301  connected to a subordinate network. 
         FIG. 12  shows an exemplary configuration of an entire system according to a third embodiment of the present invention. 
         FIG. 13  shows a processing sequence, of the third embodiment of the present invention, for detecting, from the communication apparatus  202  connected to a subordinate network, the communication apparatus  302  connected to a different subordinate network. 
         FIG. 14  shows an exemplary configuration of an entire system according to a fourth embodiment of the present invention. 
         FIG. 15  is a block diagram showing an exemplary configuration of a communication apparatus  401  according to the fourth embodiment of the present invention. 
         FIG. 16  shows a processing sequence, of the fourth embodiment of the present invention, for detecting the communication apparatus  302  connected to a private network from the communication apparatus  401  connected to a global network. 
         FIG. 17A  shows a home network comprising conventional UPnP apparatuses. 
         FIG. 17B  shows a process for detecting an UPnP apparatus in a conventional home network. 
         FIG. 18  shows a conventional router multistage home network. 
         FIG. 18B  shows a process for detecting an UPnP apparatus in a conventional home network. 
         FIG. 19A  shows a router multistage home network in which gateways each including a network connection apparatus of Patent Document 1 are provided. 
         FIG. 19B  shows a processing sequence for performing an apparatus detection by using a network connection apparatus and method of Patent Document 1. 
     
    
    
     DESCRIPTION OF THE REFERENCE CHARACTERS 
     
         
         
           
               00  global network 
               00 ,  02  private network 
               001  server 
               100 ,  200 ,  300  router 
               101 ,  202 ,  301 ,  401  communication apparatus 
               102 ,  201 ,  302  communication apparatus 
               0011  relay request transfer section 
               0012  apparatus detection response transfer section 
               0013  relay rejection response receiving section 
               0014  communication path information storage section 
               0015  communication section 
               1011 ,  2021 ,  3011 ,  4011  apparatus detection request transmission section 
               1012 ,  2022 ,  3012 ,  4012  apparatus detection response receiving section 
               1013 ,  2023 ,  3013 ,  4013  relay request transmission section 
               1014 ,  2024 ,  3014 ,  4014  relay request processing section 
               1015 ,  2025 ,  3015 ,  4015  communication section 
               1021 ,  2011 ,  3021  apparatus detection request receiving section 
               1022 ,  2012 ,  3022  apparatus detection response transmission section 
               1023 ,  2013 ,  3023  communication section 
           
         
       
    
     DETAILED DESCRIPTION OF THE INVENTION 
     First Embodiment 
     Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. 
       FIG. 1  shows an exemplary configuration of an entire system according to the first embodiment of the present invention. 
     As shown in  FIG. 1 , a global network  00  and a private network  01  are connected via a router  100 . The router  100  has a global IP address [IPW  100 ] as a WAN address, and a private IP address [IPL  100 ] as a LAN address. 
     The private network  01  and a private network  02  are connected via a router  200 . The router  200  has a private IP address [IPW  200 ] as a WAN address and a private IP address [IPL  200 ] as a LAN address. 
     A communication apparatus  101  having a private IP address [IPL  101 ] and a communication apparatus  102  having a private IP address [IPL  102 ] are connected to the private network  01 . 
     A communication apparatus  201  having a private IP address [IPL  201 ] and a communication apparatus  202  having a private IP address [IPL  202 ] are connected to the private network  02 . 
     A connection support server  001  having a private IP address [IPL  001 ] is connected to the private network  01 . The connection support server  001  has established communication paths through which the connection support server  001  can interactively communicate with all the communication apparatuses connected to the private network  01  and the private network  02 . 
       FIG. 2  is a block diagram showing an exemplary configuration of the connection support server  001  according to the first embodiment of the present invention.  FIG. 3A  is a block diagram showing an exemplary configuration of the communication apparatus  101  according to the first embodiment of the present invention.  FIG. 3B  is a block diagram showing an exemplary configuration of the communication apparatus  102  according to the first embodiment of the present invention.  FIG. 3C  is a block diagram showing an exemplary configuration of the communication apparatus  201  according to the first embodiment of the present invention.  FIG. 3D  is a block diagram showing an exemplary configuration of the communication apparatus  202  according to the first embodiment of the present invention. 
     As shown in  FIG. 2 , the connection support server  001  comprises: a relay request transfer section  0011  for, when receiving from an arbitrary communication apparatus a request to relay an apparatus detection request, transferring to a different communication apparatus the request to relay the apparatus detection request; an apparatus detection response transfer section  0012  for, when receiving an apparatus detection response, transferring the apparatus detection response to the apparatus which is a transmission source of the relay request; a relay rejection response receiving section  0013  for receiving a rejection response to the relay request for the apparatus detection request, from the communication apparatus to which the relay request has been transferred; a communication path information storage section  0014  for storing information about communication paths to all the communication apparatuses; and a communication section  0015  for performing all the communications. Mounting these functional sections on an arbitrary Internet appliance eliminates the necessity to have a dedicated apparatus which functions as the connection support server, thereby reducing a cost for a user. Note that, the connection support server  001  may not necessarily have the relay rejection response receiving section  0013 . 
     As shown in  FIG. 3A , the communication apparatus  101  comprises: an apparatus detection request transmission section  1011  for multicasting or broadcasting, on a network thereof, an apparatus detection request for an apparatus which is desired to establish a communication with the communication apparatus  101 ; a relay request transmission section  1013  for transmitting, to the connection support server  001 , a request to relay the apparatus detection request; an apparatus detection response receiving section  1012  for receiving an apparatus detection response; a relay request processing section  1014  for, when receiving from the connection support server  001  a request to relay an apparatus detection request, multicasting or broadcasting the apparatus detection request on the network of the communication apparatus  101 ; and a communication section  1015  for performing all the communications. The communication apparatus  101  is, for example, a PC or remote controller for operating another apparatus. 
     As shown in  FIG. 3B , the communication apparatus  102  comprises: an apparatus detection request receiving section  1021  for receiving an apparatus detection request which is multicasted or broadcasted on a network thereof, and determining whether or not a search target contained in the received apparatus detection request is the communication apparatus  102 ; an apparatus detection response transmission section  1022  for transmitting an apparatus detection response when the search target is the communication apparatus  102 ; and a communication section  1023  for performing all the communications. The communication apparatus  102  is, for example, a television or VCR which is operated by another apparatus. 
     As shown in  FIG. 3C , the communication apparatus  201  comprises: an apparatus detection request receiving section  2011  for receiving an apparatus detection request which is multicasted or broadcasted on a network thereof, and determining whether or not a search target contained in the received apparatus detection request is the communication apparatus  201 ; an apparatus detection response transmission section  2012  for transmitting an apparatus detection response when the search target is the communication apparatus  201 ; and a communication section  2013  for performing all the communications. The communication apparatus  201  is, for example, a television or VCR which is operated by another apparatus. 
     As shown in  FIG. 3D , the communication apparatus  202  comprises: an apparatus detection request transmission section  2021  for multicasting or broadcasting, on a network thereof, an apparatus detection request for an apparatus which is desired to establish a communication with the communication apparatus  202 ; a relay request transmission section  2023  for transmitting, to the connection support server  001 , a request to relay the apparatus detection request; an apparatus detection response receiving section  2022  for receiving an apparatus detection response; a relay request processing section  2024  for, when receiving from the connection support server  001  a request to relay an apparatus detection request, multicasting or broadcasting the apparatus detection request on the network of the communication apparatus  202 ; and a communication section  2025  for performing all the communications. The communication apparatus  202  is, for example, a PC or remote controller for operating another apparatus. 
     Described below in the present embodiment is an apparatus detection process which is performed in the case where the connection support server  001  is connected to the private network  01 . 
     Described first with reference to  FIG. 4  is a process in which the communication apparatus  101  on the private network  01  detects the communication apparatus  201  on the private network  02 . 
     The apparatus detection request transmission section  1011  of the communication apparatus  101  multicasts via the communication section  1015 , on the private network  01  to which the communication apparatus  101  is connected, an apparatus detection request which designates the communication apparatus  201  as a search target (step S 701 ). Since the communication apparatus  201  is not present on the private network  01  and the router  200  does not transfer the apparatus detection request to the private network  02 , a reception time-out occurs in the apparatus detection response receiving section  1012  for an apparatus detection response to be received from the communication apparatus  201  (step S 702 ). Thus, the apparatus detection fails (step S 703 ). 
     When the apparatus detection fails on the network of the communication apparatus  101 , the relay request transmission section  1013  of the communication apparatus  101  transmits, to the relay request transfer section  0011  of the connection support server  001  via the communication section  1015 , a request to relay the apparatus detection request (step S 704 ). 
     When the relay request transfer section  0011  receives the relay request from the communication apparatus present on the network of the connection support server  001 , the relay request transfer section  0011  selects, from the information stored in the communication path information storage section  0014 , an arbitrary apparatus of each of all the networks other than the network of the connection support server  001  (here, only the private network  02 ) (in this case, the communication apparatus  202  is selected), with which arbitrary apparatus a connection is to be established. Then, the relay request transfer section  0011  transmits, to the arbitrary apparatus via the communication section  0015 , the relay request for the apparatus detection request (step S 705 ). 
     Upon receiving the relay request from the connection support server  001 , the relay request processing section  2024  of the communication apparatus  202  extracts the search target (communication apparatus  201 ) from the relay request for the apparatus detection request (step S 706 ), and multicasts, on the private network  02 , the apparatus detection request containing the extracted information, from the apparatus detection request transmission section  2021  via the communication section  2025  (step S 707 ). 
     Upon receiving the apparatus detection request, the apparatus detection request receiving section  2011  of the communication apparatus  201  determines that the communication apparatus  201  is designated as the search target, and then transmits an apparatus detection response from the apparatus detection response transmission section  2012  to the relay request processing section  2024  of the communication apparatus  202  via the communication section  2013  (step S 708 ). 
     Upon receiving the apparatus detection response, the relay request processing section  2024  transmits the response to the apparatus detection response transfer section  0012  of the connection support server  001  (step S 709 ), and then the apparatus detection response transfer section  0012  transfers the apparatus detection response to the apparatus detection response receiving section  1012  of the communication apparatus  101  (step S 710 ). 
     By receiving the apparatus detection response at the apparatus detection response receiving section  1012  of the communication apparatus  101 , the apparatus detection succeeds in detecting the communication apparatus  201  on the different private network (step S 711 ). 
     Here, at step S 701 , at the same time as the communication apparatus  101  multicasts, on the network thereof, the apparatus detection request from the apparatus detection request transmission section  1011 , the communication apparatus  101  may transmit, from the relay request transmission section  1013  to the relay request transfer section  0011  of the connection support server  001 , the relay request for the apparatus detection request. 
     Accordingly, when an apparatus to detect is not present on the network of the communication apparatus  101 , the apparatus detection can be performed on a different network at the same time as the communication apparatus  101  waits for a response to be received. This allows a time, which is consumed until the apparatus is detected, to be reduced. 
     Further, at step S 701 , at the same time as the connection support server  001  receives the apparatus detection request multicasted from the communication apparatus  101  on the network of the server  001 , the connection support server  001  may transmit the relay request for the apparatus detection request, to an arbitrary apparatus on a different network. Operations performed at the time will hereinafter be described with reference to  FIG. 5 . 
     As shown in  FIG. 5 , the apparatus detection request transmission section  1011  of the communication apparatus  101  multicasts via the communication section  1015 , on the private network  01  to which the communication apparatus  101  is connected, an apparatus detection request designating the communication apparatus  201  as a search target (step S 801 ). Here, since the communication apparatus  201  is not present on the private network  01  and the router  200  does not transfer the apparatus detection request to the private network  02 , the apparatus detection response receiving section  1012  enters a state of waiting for an apparatus detection response to be received from the communication apparatus  201 . 
     Here, when the relay request transfer section  0011  of the connection support server  001  receives, at step S 801 , the apparatus detection request multicasted by the communication apparatus present on the network of the connection support server  001 , the relay request transfer section  0011  immediately selects, from the information stored in the communication path information storage section  0014 , an arbitrary apparatus of each of all the networks other than the network of the connection support server  001  (here, only the private network  02 ) (in this case, the communication apparatus  202  is selected), with which arbitrary apparatus a connection is to be established, and then the relay request transfer section  0011  transmits, to the arbitrary apparatus via the communication section  0015 , a relay request for the apparatus detection request (step S 802 ). 
     Upon receiving the relay request from the connection support server  001 , the relay request processing section  2024  of the communication apparatus  202  extracts the search target (communication apparatus  201 ) from the relay request for the apparatus detection request (step S 803 ), and multicasts, on the private network  02 , the apparatus detection request containing the extracted information, from the apparatus detection request transmission section  2021  via the communication section  2025  (step S 804 ). 
     Upon receiving the apparatus detection request, the apparatus detection request receiving section  2011  of the communication apparatus  201  determines that the communication apparatus  201  is designated as the search target, and then transmits an apparatus detection response from the apparatus detection response transmission section  2012  to the relay request processing section  2024  of the communication apparatus  202  via the communication section  2013  (step S 805 ). 
     Upon receiving the apparatus detection response, the relay request processing section  2024  transmits the response to the apparatus detection response transfer section  0012  of the connection support server  001  (step S 806 ), and then the apparatus detection response transfer section  0012  transfers the apparatus detection response to the apparatus detection response receiving section  1012  of the communication apparatus  101  (step S 807 ). 
     By receiving, from the connection support server  001 , the apparatus detection response at the apparatus detection response receiving section  1012  which is in the state of waiting for the apparatus detection response to be received from the communication apparatus  201 , the apparatus detection succeeds in detecting the communication apparatus  201  on the different private network (step S 808 ). 
     As described above, at the same time as an apparatus on a network waits for a response to an apparatus detection request multicasted on the network, apparatus detection can be performed on a different network. This allows a time, which is consumed when an apparatus to detect is not present on the network, to be reduced. 
     Described next with reference to  FIG. 6  is a process in which the communication apparatus  202  on the private network  02  detects the communication apparatus  102  on the private network  01 . 
     As shown in  FIG. 6 , the apparatus detection request transmission section  2021  of the communication apparatus  202  multicasts via the communication section  2025 , on the private network  02  to which the communication apparatus  202  is connected, an apparatus detection request which designates the communication apparatus  102  as a search target (step S 901 ). Here, since the communication apparatus  102  is not present on the private network  02  and the router  200  does not transfer the apparatus detection request to the private network  01 , a reception time-out occurs in the apparatus detection response receiving section  2022  for an apparatus detection response to be received from the communication apparatus  102  (step S 902 ). Thus, the apparatus detection fails (step S 903 ). 
     When the apparatus detection fails on the network of the communication apparatus  202 , the relay request transmission section  2023  of the communication apparatus  202  transmits via the communication section  2025  to the relay request transfer section  0011  of the connection support server  001 , a request to relay the apparatus detection request (step S 904 ). 
     When the relay request transfer section  0011  receives the relay request from the communication apparatus present on a different network, the relay request transfer section  0011  selects, from the information stored in the communication path information storage section  0014 , an arbitrary apparatus of each of all the networks other than the private network  02  (here, only the private network  01 ) (in this case, the communication apparatus  101  is selected), with which arbitrary apparatus a connection is to be established. Then, the relay request transfer section  0011  transmits, to the arbitrary apparatus via the communication section  0015 , the relay request for the apparatus detection request (step S 905 ). 
     Upon receiving the relay request from the connection support server  001 , the relay request processing section  1014  of the communication apparatus  101  extracts the search target (communication apparatus  102 ) from the relay request for the apparatus detection request (step S 906 ), and multicasts, on the private network  01 , the apparatus detection request containing the extracted information, from the apparatus detection request transmission section  1011  via the communication section  1015  (step S 907 ). 
     Upon receiving the apparatus detection request, the apparatus detection request receiving section  1021  of the communication apparatus  102  determines that the communication apparatus  102  is designated as the search target, and then transmits an apparatus detection response from the apparatus detection response transmission section  1022  to the relay request processing section  1014  of the communication apparatus  101  via the communication section  1023  (step S 908 ). 
     Upon receiving the apparatus detection response, the relay request processing section  1014  transmits the response to the apparatus detection response transfer section  0012  of the connection support server  001  (step S 909 ), and then the apparatus detection response transfer section  0012  transfers the apparatus detection response to the apparatus detection response receiving section  2022  of the communication apparatus  202  (step S 910 ). 
     By receiving the apparatus detection response at the apparatus detection response receiving section  2022  of the communication apparatus  202 , the apparatus detection succeeds in detecting the communication apparatus  102  on the different private network (step S 911 ). 
     Upon receiving, at step S 904 , the relay request for the apparatus detection request, the connection support server  001  may multicast the apparatus detection request on the network of the connection support server  001 , instead of transferring the relay request to the arbitrary apparatus on the network. Operations performed at the time will be described with reference to  FIG. 7 . 
     Processing performed at steps S 1001  to S 1004  in  FIG. 7  is the same as that performed at steps S 901  to S 904  in  FIG. 6 . 
     Upon receiving the relay request for the apparatus detection request at step S 1004 , the relay request transfer section  0011  of the connection support server  001  multicasts, on the network of the connection support server  001  via the communication section  0015 , the apparatus detection request for the apparatus which is the search target contained in the relay request (i.e., the communication apparatus  102 ) (step S 1005 ). 
     Upon receiving the apparatus detection request, the apparatus detection request receiving section  1021  of the communication apparatus  102  determines that the communication apparatus  102  is designated as the search target, and then transmits, via the communication section  1023 , an apparatus detection response from the apparatus detection response transmission section  1022  to the apparatus detection response transfer section  0012  of the connection support server  001  (step S 1006 ). 
     Upon receiving the apparatus detection response, the apparatus detection response transfer section  0012  transmits, via the communication section  0015 , the apparatus detection response to the apparatus detection response receiving section  2022  of the communication apparatus  202  which is a transmission source of the relay request (step S 1007 ). 
     By receiving the apparatus detection response at the apparatus detection response receiving section  2022  of the communication apparatus  202 , the apparatus detection succeeds in detecting the communication apparatus  102  on the different private network (step S 1008 ). 
     As described above, the connection support server  001  multicasts the apparatus detection request on the network of the connection support server  001 , instead of transferring the relay request to an arbitrary apparatus on the network. This omits the steps in which the apparatus detection request is relayed to the arbitrary apparatus on the network of the connection support server  001  and the arbitrary apparatus performs multicasting. Accordingly, a time consumed for the search can be reduced. 
     Note that, the relay request transfer section  0011  of the connection support server  001  which has received, from the communication apparatus on the different network at step S 904  of  FIG. 6 , the relay request for the apparatus detection request, selects, from the information stored in the communication path information storage section  0014 , an arbitrary apparatus of each of all the networks other than the private network  02  (here, only the private network  01 ) (in this case, the communication apparatus  101  is selected), with which arbitrary apparatus a connection is to be established. Then, the relay request transfer section  0011  transmits, to the arbitrary apparatus via the communication section  0015 , the relay request for the apparatus detection request. Here, the relay request may be always transmitted to the same communication apparatus. For example, by always causing an apparatus having a high processing capability to multicast the apparatus detection request, such processing load can be prevented from being imposed on an apparatus having a low processing capability. 
     Further, the relay request transfer section  0011  of the connection support server  001  which has received, from the communication apparatus on the different network, the relay request for the apparatus detection request may transmit the relay request for the apparatus detection request, to a different communication apparatus each time the relay request transfer section  0011  transmits the relay request. As a result, the multicasting of the apparatus detection request can be performed in a dispersed manner, whereby stability of the network is obtained. 
     The communication apparatus, which has received the relay request at step S 705  of  FIG. 4 , step S 802  of  FIG. 5  or step S 905  of  FIG. 6 , may transmit, in consideration of processing load thereon, a relay rejection response from a relay rejection response transmission section (not shown) to the relay rejection response receiving section  0013  of the connection support server  001 . The relay rejection response receiving section  0013 , which has received the relay rejection response, retransmits the relay request to a communication apparatus which is stored in the communication path information storage section  0014  and which is different from the apparatus which is a transmission source of the relay rejection response. This prevents the apparatus from becoming incapable of performing processing due to performing the relay processing. 
     Used as a message of an apparatus detection request may be an M-SEARCH request stipulated by UPnP, or may be a message stipulated by a different protocol. 
     The transmission manner of the apparatus detection request is not limited to multicasting. The transmission manner may be broadcasting or any other manner of data transmission. 
     The configuration described in the present embodiment is merely an example, and the present embodiment is not limited thereto. 
     For example, in the case where the connection support server  001  is connected to the private network  02 , the communication apparatus  201  can be detected from the communication apparatus  101 , and also the communication apparatus  102  can be detected from the communication apparatus  202 , by performing the same processing as described above. 
     It is assumed in the present embodiment that all the communication apparatuses each have a communication path established with the connection support server  001 . However, the present embodiment is not limited thereto. As long as there is, on a private network, at least one communication apparatus which has a communication path established with the connection support server  001 , even a communication apparatus which does not have a communication path established with the connection support server  001  can be detected by causing the at least one communication apparatus having the established communication path to perform the relaying in accordance with the processing sequence described in the present embodiment. 
     Second Embodiment 
     Hereinafter, a second embodiment of the present invention will be described with reference to the drawings. 
       FIG. 8  shows an exemplary configuration of an entire system according to the second embodiment of the present invention. 
     As shown in  FIG. 8 , the global network  00  and the private network  01  are connected via the router  100 . The router  100  has the global IP address [IPW  100 ] as a WAN address and the private IP address [IPL  100 ] as a LAN address. 
     Also, the private network  01  and the private network  02  are connected via the router  200 . The router  200  has the private IP address [IPW  200 ] as a WAN address and the private IP address [IPL  200 ] as a LAN address. 
     Further, the private network  02  and a private network  03  are connected via a router  300 . The router  300  has a private IP address [IPW  300 ] as a WAN address and a private IP address [IPL  300 ] as a LAN address. 
     The communication apparatus  101  having the private IP address [IPL  101 ] and the communication apparatus  102  having the private IP address [IPL  102 ] are connected to the private network  01 . 
     The communication apparatus  201  having the private IP address [IPL  201 ] and the communication apparatus  202  having the private IP address [IPL  202 ] are connected to the private network  02 . 
     A communication apparatus  301  having a private IP address [IPL  301 ] and a communication apparatus  302  having a private IP address [IPL  302 ] are connected to the private network  03 . 
     The connection support server  001  having the private IP address [IPL  001 ] is also connected to the private network  02 . The connection support server  001  has established communication paths through which the connection support server  001  can interactively communicate with all the communication apparatuses connected to the private networks  01 ,  02  and  03 . 
     Block diagrams showing the configurations of the connection support server  001  and the communication apparatuses  101 ,  102 ,  201  and  202  are the same as those described in the first embodiment. 
       FIG. 9A  is a block diagram showing an exemplary configuration of the communication apparatus  301  according to the second embodiment of the present invention.  FIG. 9B  is a block diagram showing an exemplary configuration of the communication apparatus  302  according to the second embodiment of the present invention. 
     As shown in  FIG. 9A , the communication apparatus  301  comprises: an apparatus detection request transmission section  3011  for multicasting, on a network thereof, an apparatus detection request for an apparatus which is desired to establish a communication with the communication apparatus  301 ; an apparatus detection response receiving section  3012  for receiving an apparatus detection response; a relay request transmission section  3013  for transmitting, to the connection support server  001 , a request to relay the apparatus detection request; a relay request processing section  3014  for, when receiving from the connection support server  001  a request to relay an apparatus detection request, multicasting the apparatus detection request on the network of the communication apparatus  301 ; and a communication section  3015  for performing all the communications. The communication apparatus  301  is, for example, a PC or remote controller for operating another apparatus. 
     As shown in  FIG. 9B , the communication apparatus  302  comprises: an apparatus detection request receiving section  3021  for receiving an apparatus detection request which is multicasted on a network thereof, and determining whether or not a search target contained in the received apparatus detection request is the communication apparatus  302 ; an apparatus detection response transmission section  3022  for transmitting an apparatus detection response when the search target is the communication apparatus  302 ; and a communication section  3023  for performing all the communications. The communication apparatus  302  is, for example, a television or VCR which is operated by another apparatus. 
     Described below in the present embodiment is an apparatus detection process which is performed in the case where the connection support server  001  is connected to the private network  02 . 
     Described first with reference to  FIG. 10  is a process in which the communication apparatus  101  on the private network  01  detects the communication apparatus  201  on the private network  02 . 
     The apparatus detection request transmission section  1011  of the communication apparatus  101  multicasts via the communication section  1015 , on the private network  01  to which the communication apparatus  101  is connected, an apparatus detection request which designates the communication apparatus  201  as a search target (step S 1301 ). Here, since the communication apparatus  201  is not present on the private network  01  and the router  200  does not transfer the apparatus detection request to the private network  02 , a reception time-out occurs in the apparatus detection response receiving section  1012  for an apparatus detection response to be received from the communication apparatus  201  (step S 1302 ). Thus, the apparatus detection fails (step S 1303 ). 
     When the apparatus detection fails on the network of the communication apparatus  101 , the relay request transmission section  1013  of the communication apparatus  101  transmits, to the relay request transfer section  0011  of the connection support server  001  via the communication section  1015 , a request to relay the apparatus detection request (step S 1304 ). 
     When the relay request transfer section  0011  receives the relay request from the communication apparatus  101  present on a different network (private network  01 ), the relay request transfer section  0011  selects, from the information stored in the communication path information storage section  0014 , an arbitrary apparatus of each of all the networks other than the private network  01  (here, the private network  02  and the private network  03 ) (in this case, the communication apparatus  202  and the communication apparatus  301  are selected), with which arbitrary apparatus a connection is to be established. Then, the relay request transfer section  0011  transmits, to the arbitrary apparatus via the communication section  0015 , the relay request for the apparatus detection request (step S 1305 ). 
     Upon receiving the relay request from the connection support server  001 , the relay request processing section  2024  of the communication apparatus  202  extracts the search target (communication apparatus  201 ) from the relay request for the apparatus detection request (step S 1306 ), and multicasts, on the private network  02 , the apparatus detection request containing the extracted information, from the apparatus detection request transmission section  2021  via the communication section  2025  (step S 1307 ). 
     Similarly, Upon receiving the relay request from the connection support server  001 , the relay request processing section  3014  of the communication apparatus  301  extracts the search target (communication apparatus  201 ) from the relay request for the apparatus detection request (step S 1308 ), and multicasts, on the private network  03 , the apparatus detection request containing the extracted information, from the apparatus detection request transmission section  3011  via the communication section  3015  (step S 1309 ). 
     Here, since the communication apparatus  201  is not present on the private network  03 , and the router  300  does not transfer the apparatus detection request to the private network  02 , a reception time-out occurs for an apparatus detection response to be received from the communication apparatus  201  (step S 1310 ). 
     Upon receiving the apparatus detection request multicasted by the communication apparatus  202 , the apparatus detection request receiving section  2011  of the communication apparatus  201  determines that the communication apparatus  201  is designated as the search target, and then transmits an apparatus detection response from the apparatus detection response transmission section  2012  to the relay request processing section  2024  of the communication apparatus  202  via the communication section  2013  (step S 1311 ). 
     Upon receiving the apparatus detection response, the relay request processing section  2024  transmits the response to the apparatus detection response transfer section  0012  of the connection support server  001  (step S 1312 ), and then the apparatus detection response transfer section  0012  transfers the apparatus detection response to the apparatus detection response receiving section  1012  of the communication apparatus  101  (step S 1313 ). 
     By receiving the apparatus detection response at the apparatus detection response receiving section  1012  of the communication apparatus  101 , the apparatus detection succeeds in detecting the communication apparatus  201  on the different private network (step S 1314 ). 
     Here, at step S 1301 , at the same time as the communication apparatus  101  multicasts, on the network thereof, the apparatus detection request from the apparatus detection request transmission section  1011 , the communication apparatus  101  may transmit, from the relay request transmission section  1013  to the relay request transfer section  0011  of the connection support server  001 , the relay request for the apparatus detection request. Accordingly, when an apparatus to detect is not present on the network of the communication apparatus  101 , the apparatus detection can be performed on different networks at the same time as the communication apparatus  101  waits for a response to be received. This allows a time, which is consumed until the apparatus is detected, to be reduced. 
     Upon receiving, at step S 1304 , the relay request for the apparatus detection request, the connection support server  001  may multicast the apparatus detection request on the network of the connection support server  001 , instead of transferring the relay request to the arbitrary apparatus on the network. Since operations performed at the time are the same as the processing shown in  FIG. 7  of the first embodiment, a description thereof will be omitted. In the above manner, the steps in which the apparatus detection request is relayed to the arbitrary apparatus on the network of the connection support server  001  and the apparatus performs multicasting, can be omitted. Accordingly, a time consumed for the search can be reduced. 
     Described next with reference to  FIG. 11  is a process in which the communication apparatus  301  on the private network  03  detects the communication apparatus  102  on the private network  01 . 
     As shown in  FIG. 11 , the apparatus detection request transmission section  3011  of the communication apparatus  301  multicasts via the communication section  3015 , on the private network  03  to which the communication apparatus  301  is connected, an apparatus detection request which designates the communication apparatus  102  as a search target (step S 1401 ). Here, since the communication apparatus  102  is not present on the private network  03 , and the router  200  does not transfer the apparatus detection request to the private network  02 , a reception time-out occurs in the apparatus detection response receiving section  3012  for an apparatus detection response to be received from the communication apparatus  102  (step S 1402 ). Thus, the apparatus detection fails (step S 1403 ). 
     When the apparatus detection fails on the network of the communication apparatus  301 , the relay request transmission section  3013  of the communication apparatus  301  transmits, to the relay request transfer section  0011  of the connection support server  001  via the communication section  3015 , a request to relay the apparatus detection request (step S 1404 ). 
     When the relay request transfer section  0011  receives the relay request from the communication apparatus  301  present on a different network (private network  03 ), the relay request transfer section  0011  selects, from the information stored in the communication path information storage section  0014 , an arbitrary apparatus of each of all the networks other than the private network  03  (here, the private network  01  and the private network  02 ) (in this case, the communication apparatus  101  and the communication apparatus  202  are selected), with which arbitrary apparatus a connection is to be established. Then, the relay request transfer section  0011  transmits, to the arbitrary apparatus via the communication section  0015 , the relay request for the apparatus detection request (step S 1405 ). 
     Upon receiving the relay request from the connection support server  001 , the relay request processing section  1014  of the communication apparatus  101  extracts the search target (communication apparatus  102 ) from the relay request for the apparatus detection request (step S 1406 ), and multicasts, on the private network  01 , the apparatus detection request containing the extracted information, from the apparatus detection request transmission section  1011  via the communication section  1015  (step S 1407 ). 
     Similarly, Upon receiving the relay request from the connection support server  001 , the relay request processing section  2024  of the communication apparatus  202  extracts the search target (communication apparatus  102 ) from the relay request for the apparatus detection request (step S 1408 ), and multicasts, on the private network  02 , the apparatus detection request containing the extracted information, from the apparatus detection request transmission section  2021  via the communication section  2025  (step S 1409 ). 
     Here, since the communication apparatus  102  is not present on the private network  02  and the router  200  does not transfer the apparatus detection request to the private network  01 , a reception time-out occurs for an apparatus detection response to be received from the communication apparatus  102  (step S 1410 ). 
     Upon receiving the apparatus detection request multicasted by the communication apparatus  101 , the apparatus detection request receiving section  1021  of the communication apparatus  102  determines that the communication apparatus  102  is designated as the search target, and then transmits an apparatus detection response from the apparatus detection response transmission section  1022  to the relay request processing section  1014  of the communication apparatus  101  via the communication section  1023  (step S 1411 ). 
     Upon receiving the apparatus detection response, the relay request processing section  1014  transmits the response to the apparatus detection response transfer section  0012  of the connection support server  001  (step S 1412 ), and then the apparatus detection response transfer section  0012  transfers the apparatus detection response to the apparatus detection response receiving section  3012  of the communication apparatus  301  (step S 1413 ). 
     By receiving the apparatus detection response at the apparatus detection response receiving section  3012  of the communication apparatus  301 , the apparatus detection succeeds in detecting the communication apparatus  102  on the different private network (step S 1414 ). 
     Note that, when the relay request transfer section  0011  of the connection support server  001  receives, from the communication apparatus on the different network at step S 1404  of  FIG. 11 , the relay request for the apparatus detection request, the relay request transfer section  0011  selects, from the information stored in the communication path information storage section  0014 , an arbitrary apparatus of each of all the networks other than the private network  03  (here, the private network  01  and the private network  02 ) (in this case, the communication apparatus  101  and the communication apparatus  202  are selected), and then transmits, to the arbitrary apparatus via the communication section  0015 , the relay request for the apparatus detection request. Here, the relay request may be always transmitted to the same communication apparatus. For example, by always causing an apparatus having a high processing capability to multicast the apparatus detection request, a time consumed for the search can be reduced. 
     Further, the relay request transfer section  0011  of the connection support server  001  which has received, from the communication apparatus on the different network, the relay request for the apparatus detection request may transmit the relay request to a different communication apparatus each time the relay request transfer section  0011  transmits the relay request. As a result, the multicasting of the apparatus detection request can be performed in a dispersed manner, whereby stability of the network is obtained. 
     The communication apparatuses having received the relay request at step S 1305  of  FIG. 10  or at step S 1405  of  FIG. 11  may each transmit, in consideration of processing load thereon, a relay rejection response from the relay rejection response transmission section (not shown) to the relay rejection response receiving section  0013  of the connection support server  001 . The relay rejection response receiving section  0013 , which has received the relay rejection response, retransmits the relay request to a communication apparatus which is stored in the communication path information storage section and which is different from the apparatus which is a transmission source of the relay rejection response. This makes it possible to, in the case where the apparatus which is requested to relay the apparatus detection request is unable to multicast the apparatus detection request due to a load imposed thereon, request a different apparatus, on which a processing load is not imposed, to relay the apparatus detection request. This prevents the apparatus from becoming incapable of performing processing. 
     Used as a message of an apparatus detection request may be an M-SEARCH request stipulated by UPnP, or may be a message stipulated by a different protocol. 
     The transmission manner of the apparatus detection request is not limited to multicasting. The transmission manner may be broadcasting or any other manner of data transmission. 
     The configuration described in the present embodiment is merely an example, and the present embodiment is not limited thereto. 
     For example, in the case where the connection support server  001  is connected to the private network  02 , the communication apparatus  302  can be detected from the communication apparatus  101 , and also the communication apparatus  102  or  302  can be detected from the communication apparatus  202 , by performing the same processing as described above. 
     Further, in the case where the connection support server  001  is connected to the private network  01 , an apparatus on the private network  02  or  03  can be detected from an apparatus on the private network  01 ; an apparatus on the private network  01  or  03  can be detected from an apparatus on the private network  02 ; and an apparatus on the private network  01  or  02  can be detected from an apparatus on the private network  03 . 
     It is assumed in the present embodiment that all the communication apparatuses each have an established communication path with the connection support server  001 . However, the present embodiment is not limited thereto. As long as there is, on a private network, at least one communication apparatus which has an established communication path with the connection support server  001 , even a communication apparatus which does not have an established communication path with the connection support server  001  can be detected by causing the at least one communication apparatus having the established communication path to perform the relaying in accordance with the processing sequence described in the present embodiment. 
     Third Embodiment 
     Hereinafter, a third embodiment of the present invention will be described with reference to the drawings. 
       FIG. 12  shows an exemplary configuration of an entire system according to the third embodiment of the present invention. 
     As shown in  FIG. 12 , the global network  00  and the private network  01  are connected via the router  100 . The router  100  has the global IP address [IPW  100 ] as a WAN address and the private IP address [IPL  100 ] as a LAN address. 
     Also, the private network  01  and the private network  02  are connected via the router  200 . The router  200  has the private IP address [IPW  200 ] as a WAN address and the private IP address [IPL  200 ] as a LAN address. 
     Further, the private network  01  and the private network  03  are connected via the router  300 . The router  300  has the private IP address [IPW  300 ] as a WAN address and the private IP address [IPL  300 ] as a LAN address. 
     The communication apparatus  201  having the private IP address [IPL  201 ] and the communication apparatus  202  having the private IP address [IPL  202 ] are connected to the private network  02 . 
     The communication apparatus  301  having the private IP address [IPL  301 ] and the communication apparatus  302  having the private IP address [IPL  302 ] are connected to the private network  03 . 
     The connection support server  001  having the private IP address [IPL  001 ] is also connected to the private network  01 . The connection support server  001  has established communication paths through which the connection support server  001  can interactively communicate with all the communication apparatuses connected to the private networks  02  and  03 . 
     Block diagrams showing the configurations of the connection support server  001  and the communication apparatuses  201 ,  202 ,  301  and  302  are the same as those described in the first and second embodiments. 
     Described below in the present embodiment is an apparatus detection process which is performed in the case where the connection support server  001  is connected to the private network  01 . 
     Described first with reference to  FIG. 13  is a process in which the communication apparatus  202  on the private network  02  detects the communication apparatus  302  on the private network  03 . 
     As shown in  FIG. 13 , the apparatus detection request transmission section  2021  of the communication apparatus  202  multicasts via the communication section  2025 , on the private network  02  to which the communication apparatus  202  is connected, an apparatus detection request which designates the communication apparatus  302  as a search target (step S 1601 ). Here, since the communication apparatus  302  is not present on the private network  02  and the router  200  does not transfer the apparatus detection request to the private network  01 , a reception time-out occurs in the apparatus detection response receiving section  2022  for an apparatus detection response to be received from the communication apparatus  302  (step S 1602 ). Thus, the apparatus detection fails (step S 1603 ). 
     When the apparatus detection fails on the network of the communication apparatus  202 , the relay request transmission section  2023  of the communication apparatus  202  transmits, to the relay request transfer section  0011  of the connection support server  001  via the communication section  2025 , a request to relay the apparatus detection request (step S 1604 ). 
     When the relay request transfer section  0011  receives the relay request from the communication apparatus present on a different network (private network  02 ), the relay request transfer section  0011  selects, from the information stored in the communication path information storage section  0014 , an arbitrary apparatus of each of all the networks other than the private network  02  (here, the private network  01  and the private network  03 ) (in this case, only the communication apparatus  301  is selected since there is no communication apparatus present on the private network  01 ), with which arbitrary apparatus a connection is to be established. Then, the relay request transfer section  0011  transmits, to the arbitrary apparatus via the communication section  0015 , the relay request for the apparatus detection request (step S 1605 ). 
     Upon receiving the relay request from the connection support server  001 , the relay request processing section  3014  of the communication apparatus  301  extracts the search target (communication apparatus  302 ) from the relay request for the apparatus detection request (step S 1606 ), and multicasts, on the private network  03 , the apparatus detection request containing the extracted information, from the apparatus detection request transmission section  3011  via the communication section  3015  (step S 1607 ). 
     Upon receiving the apparatus detection request, the apparatus detection request receiving section  3021  of the communication apparatus  302  determines that the communication apparatus  302  is designated as the search target, and then transmits an apparatus detection response from the apparatus detection response transmission section  3022  to the relay request processing section  3014  of the communication apparatus  301  via the communication section  3023  (step S 1608 ). 
     Upon receiving the apparatus detection response, the relay request processing section  3014  transmits the response to the apparatus detection response transfer section  0012  of the connection support server  001  (step S 1609 ), and then the apparatus detection response transfer section  0012  transfers the apparatus detection response to the apparatus detection response receiving section  2022  of the communication apparatus  202  (step S 1610 ). 
     By receiving the apparatus detection response at the apparatus detection response receiving section  2022  of the communication apparatus  202 , the apparatus detection succeeds in detecting the communication apparatus  302  on the different private network (step S 1611 ). 
     Here, at step S 1601 , at the same time as the communication apparatus  202  multicasts, on the network thereof, the apparatus detection request from the apparatus detection request transmission section  2021 , the communication apparatus  202  may transmit, from the relay request transmission section  2023  to the relay request transfer section  0011  of the connection support server  001 , the relay request for the apparatus detection request. Accordingly, when an apparatus to detect is not present on the network of the communication apparatus  202 , the apparatus detection can be performed on a different network at the same time as the communication apparatus  202  waits for a response to be received. This allows a time, which is consumed until the apparatus is detected, to be reduced. 
     Used as a message of an apparatus detection request may be an M-SEARCH request stipulated by UPnP, or may be a message stipulated by a different protocol. 
     The transmission manner of the apparatus detection request is not limited to multicasting. The transmission manner may be broadcasting or any other manner of data transmission. 
     The configuration described in the present embodiment is merely an example, and the present embodiment is not limited thereto. 
     For example, in the case where the connection support server  001  is connected to the private network  02 , an apparatus on the private network  03  can be detected from an apparatus on the private network  02  by performing the same processing as described above. Also, an apparatus on the private network  02  can be detected from an apparatus on the private network  03 . 
     The same is true in the case where the connection support server is connected to the private network  03 . 
     It is assumed in the present embodiment that all the communication apparatuses each have an established communication path with the connection support server  001 . However, the present embodiment is not limited thereto. As long as there is, on a private network, at least one communication apparatus which has an established communication path with the connection support server  001 , even a communication apparatus which does not have an established communication path with the connection support server  001  can be detected by causing the at least one communication apparatus having the established communication path to perform the relaying in accordance with the processing sequence described in the present embodiment. 
     Fourth Embodiment 
     Hereinafter, a fourth embodiment of the present invention will be described with reference to the drawings. 
       FIG. 14  shows an exemplary configuration of an entire system according to the fourth embodiment of the present invention. As shown in  FIG. 14 , the global network  00  and the private network  01  are connected via the router  100 . The router  100  has the global IP address [IPW  100 ] as a WAN address and the private IP address [IPL  100 ] as a LAN address. 
     Also, the private network  01  and the private network  02  are connected via the router  200 . The router  200  has the private IP address [IPW  200 ] as a WAN address and the private IP address [IPL  200 ] as a LAN address. 
     Further, the private network  01  and the private network  03  are connected via the router  300 . The router  300  has the private IP address [IPW  300 ] as a WAN address and the private IP address [IPL  300 ] as a LAN address. 
     A communication apparatus  401  having a global IP address [IPW  401 ] is connected to the global network  00 . 
     The communication apparatus  201  having the private IP address [IPL  201 ] and the communication apparatus  202  having the private IP address [IPL  202 ] are connected to the private network  02 . 
     The communication apparatus  301  having the private IP address [IPL  301 ] and the communication apparatus  302  having the private IP address [IPL  302 ] are connected to the private network  03 . 
     The connection support server  001  having the private IP address [IPL  001 ] is also connected to the private network  01 . The connection support server  001  has established communication paths through which the connection support server  001  can interactively communicate with all the communication apparatuses connected to the global network  00 , the private network  02  and the private network  03 . 
     Block diagrams showing the configurations of the connection support server  001  and the communication apparatuses  201 ,  202 ,  301  and  302  are the same as those described in the first and second embodiments. 
       FIG. 15  is a block diagram showing an exemplary configuration of the communication apparatus  401  according to the fourth embodiment of the present invention. As shown in  FIG. 15  the communication apparatus  401  comprises: an apparatus detection request transmission section  4011  for multicasting, on a network thereof, an apparatus detection request for an apparatus which is desired to establish a communication with the communication apparatus  401 ; an apparatus detection response receiving section  4012  for receiving an apparatus detection response; a relay request transmission section  4013  for transmitting, to the connection support server, a request to relay the apparatus detection request; a relay request processing section  4014  for, when receiving from the connection support server  001  a request to relay an apparatus detection request, multicasting the apparatus detection request on the network of the communication apparatus  401 ; and a communication section  4015  for performing all the communications. The communication apparatus  401  is, for example, a mobile terminal having communication functions such as a mobile phone or PDA which is for operating another apparatus. 
     Since the communication apparatus  401  having the global IP address is unable to perform a request transmission by multicasting on the global network, the communication apparatus  401  may not necessarily have the apparatus detection request transmission section  4011  and the relay request processing section  4014 . 
     Described below in the present embodiment is an apparatus detection process which is performed in the case where the connection support server  001  is connected to the private network  01 . 
     Described first with reference to  FIG. 16  is a process in which the communication apparatus  401  on the global network  00  detects the communication apparatus  302  on the private network  03 . 
     Since the network to which the communication apparatus  401  is connected is a global network, the communication apparatus  401  does not multicast an apparatus detection request, and the relay request transmission section  4013  of the communication apparatus  401  transmits, to the relay request transfer section  0011  of the connection support server  001  via the communication section  4015 , a relay request for an apparatus detection request (step S 1901 ). 
     When the relay request transfer section  0011  receives the relay request from the communication apparatus present on a different network (global network  00 ), the relay request transfer section  0011  selects, from the information stored in the communication path information storage section  0014 , an arbitrary apparatus of each of all the networks other than the global network  00  (here, the private networks  01 ,  02  and  03 ) (in this case, the communication apparatuses  201  and  301  are selected since there is no communication apparatus on the private network  01 ), with which arbitrary apparatus a connection is to be established. Then, the relay request transfer section  0011  transmits, to the arbitrary apparatus via the communication section  0015 , the relay request for the apparatus detection request (step S 1902 ). 
     Upon receiving the relay request from the connection support server  001 , the relay request processing section  2024  of the communication apparatus  202  extracts the search target (communication apparatus  302 ) from the relay request for the apparatus detection request (step S 1903 ), and multicasts, on the private network  02 , the apparatus detection request containing the extracted information, from the apparatus detection request transmission section  2021  via the communication section  2025  (step S 1904 ). 
     Since the communication apparatus  201  having received the apparatus detection request is not designated as the search target, the apparatus detection request receiving section  2011  of the communication apparatus  201  does not transmit an apparatus detection response. 
     Upon receiving the relay request from the connection support server  001 , the relay request processing section  3014  of the communication apparatus  301  extracts the search target (communication apparatus  302 ) from the relay request for the apparatus detection request (step S 1905 ), and multicasts, on the private network  03 , the apparatus detection request containing the extracted information, from the apparatus detection request transmission section  3011  via the communication section  3015  (step S 1906 ). 
     Upon receiving the apparatus detection request, the apparatus detection request receiving section  3021  of the communication apparatus  302  determines that the communication apparatus  302  is designated as the search target, and then transmits an apparatus detection response from the apparatus detection response transmission section  3022  to the relay request processing section  3014  of the communication apparatus  301  via the communication section  3023  (step S 1907 ). 
     Upon receiving the apparatus detection response, the relay request processing section  3014  transmits the response to the apparatus detection response transfer section  0012  of the connection support server  001  (step S 1908 ), and then the apparatus detection response transfer section  0012  transfers the apparatus detection response to the apparatus detection response receiving section  4012  of the communication apparatus  401  (step S 1909 ). 
     By receiving the apparatus detection response at the apparatus detection response receiving section  4012  of the communication apparatus  401 , the apparatus detection succeeds in detecting the communication apparatus  302  on the different private network (step S 1910 ). 
     Used as a message of an apparatus detection request may be an M-SEARCH request stipulated by UPnP, or may be a message stipulated by a different protocol. 
     The transmission manner of the apparatus detection request is not limited to multicasting. The transmission manner may be broadcasting or any other manner of data transmission. 
     The configuration described in the present embodiment is merely an example, and the present embodiment is not limited thereto. 
     For example, in the case where the connection support server  001  is connected to the private network  02 , an apparatus on the private network  02  or  03  can be detected from an apparatus on the global network  00  by performing the same processing as described above. Also, an apparatus on the global network  00  can be detected from an apparatus on the private network  02  or  03 . 
     The same is true in the case where the connection support server is connected to the private network  03 . 
     Further, in the present embodiment, the communication apparatus  401  on the global network  00  has a global IP address and is directly connected to the global network  00 . However, even in the case where the communication apparatus  401  is connected to a relay device having a global IP address such as a router and has a private IP address, the apparatus detection can be performed in the same manner. 
     It is assumed in the present embodiment that all the communication apparatuses each have an established communication path with the connection support server  001 . However, the present embodiment is not limited thereto. By causing a communication apparatus having an established communication path with the connection support server  001  to perform the relaying in accordance with the processing sequence described in the present embodiment, even a communication apparatus, which is connected to a same network as that of the communication apparatus and which does not have an established communication path with the connection support server  001 , can be detected. 
     INDUSTRIAL APPLICABILITY 
     The communication apparatus of the present invention is useful for, e.g., detecting an apparatus present on a different network in, e.g., a router multistage network comprising a plurality of routers.