Patent Publication Number: US-2015085781-A1

Title: Communication Apparatus, Communication Method, Communication System, Control Apparatus and Program

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present invention is based upon and claims the benefit of the priority of Japanese Patent Application No. 2012-102577, filed on Apr. 27, 2012, the disclosure of which is incorporated herein in its entirety by reference thereto. 
     FIELD 
     The present invention relates to a communication apparatus, a communication method, a communication system, a control apparatus and a program, and in particular to a communication apparatus, a communication method, a communication system, a control apparatus and a program, which perform communication by at least one of a plurality of communication schemes. 
     BACKGROUND 
     In recent years, it has become possible for mobile terminals to connect to a plurality of types of RAT (Radio Access Technology). For example, a mobile terminal can connect to a plurality of RATs such as 3GPP (Third Generation Partnership Project) access including UTRAN (UMTS Terrestrial Radio Access Network) and LTE (Long Term Evolution), and WLAN (Wireless Local Area Network) including 802.11g and 802.11n, or the like. 
     Patent Literature PTL 1 (Japanese Translation of PCT International Publication, Publication No. 2011-524686) discloses an apparatus that decides which access network to use, among a plurality of access networks (namely, a plurality of RATs). 
     Patent Literature PTL 2 (Japanese Patent Kokai Publication No. 2011-217174) discloses technology for connecting to a dedicated network from a terminal connected to the Internet. 
     CITATION LIST 
     Patent Literature 
     [PTL 1] 
     Japanese Patent Kohyo Publication No. JP2011-524686A 
     [PTL 2] 
     Japanese Patent Kokai Publication No. JP2011-217174A 
     SUMMARY 
     Technical Problem 
     The entire disclosures of the above Patent Literatures PTL 1 and PTL 2 are incorporated herein by reference thereto. The following analyses are given by the present invention. The above Patent Literature PTL 1 and PTL 2 do not disclose how a communication terminal handles a case where a plurality of communication addresses from a plurality of RATs are assigned to the communication terminal. 
     In a case of communicating with a plurality of RATs, it is assumed that with regard to a communication apparatus (such as a communication terminal), a plurality of communication addresses are assigned from the plurality of RATs. In the case where a plurality of communication addresses are assigned, if the communication apparatus does not handle the determination of an address to be used, among the plurality of communication addresses, there is a possibility of a failure occurring in communication. 
     Solution to Problem 
     According to a first aspect of the present invention, there is provided a communication apparatus, comprising: communication means (unit) that communicates with a network by at least one of a plurality of communication schemes; and control means (unit) that disguises a first communication address corresponding to a first communication scheme, by a second communication address corresponding to a second communication scheme, based on an instruction transmitted from a control apparatus. 
     According to a second aspect of the present invention, there is provided a communication method, the method comprising: 
     using a communication apparatus that communicates with a network by at least one of a plurality of communication schemes;
 
disguising a first communication address corresponding to a first communication scheme, by a second communication address corresponding to a second communication scheme, based on an instruction transmitted from a control apparatus; and
 
communicating using the disguised communication address.
 
     According to a third aspect of the present invention, there is provided a communication system, the system comprising: 
     at least one communication apparatus; and
 
a control apparatus that controls packet processing by the communication apparatus; wherein
 
the communication apparatus comprises:
 
communication means (unit) that communicates with a network by at least one of a plurality of communication schemes; and
 
control means (unit) that disguises a first communication address corresponding to a first communication scheme, by a second communication address corresponding to a second communication scheme, based on an instruction transmitted from the control apparatus.
 
     According to a fourth aspect of the present invention, there is provided a control apparatus, the control apparatus comprising: 
     means (unit) that communicates with a communication apparatus that uses at least one of a plurality of communication schemes; and
 
means (unit) that transmits to the communication apparatus an instruction to disguise a first communication address corresponding to a first communication scheme, by a second communication address corresponding to a second communication scheme.
 
     According to a fifth aspect of the present invention, there is provided a communication method, the method comprising: 
     communicating with a communication apparatus that uses at least one of a plurality of communication schemes; and
 
transmitting to the communication apparatus an instruction to disguise a first communication address corresponding to a first communication scheme, by a second communication address corresponding to a second communication scheme.
 
     According to a sixth aspect of the present invention, there is provided a program, the program causing a communication apparatus that communicates with a network by at least one of a plurality of communication schemes to execute: 
     disguising a first communication address corresponding to a first communication scheme, by a second communication address corresponding to a second communication scheme, based on an instruction transmitted from a control apparatus. 
     There is also provided a non-transitory computer-readable recording medium storing the program. 
     Advantageous Effects of Invention 
     A communication apparatus of the present invention, with regard to a plurality of communication addresses being assigned from a plurality of RATs, can perform communication with a network without being aware of which address should be used. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram showing a system configuration example of a first exemplary embodiment. 
         FIG. 2  is a sequence diagram showing an operation example of the first exemplary embodiment. 
         FIG. 3  is a diagram showing a configuration example of a communication apparatus of the first exemplary embodiment. 
         FIG. 4  is a diagram showing an example of functionality of a control unit. 
         FIG. 5  is a diagram showing an example of functionality of the control unit. 
         FIG. 6  is a sequence diagram showing an operation example of the first exemplary embodiment. 
         FIG. 7  is a diagram showing a configuration example of a control apparatus. 
         FIG. 8  is a diagram showing an example of information communicated by the communication apparatus to the control apparatus. 
         FIG. 9  is an example of a database held by a management DB of the control apparatus. 
         FIG. 10  is a diagram showing a configuration example of a communication apparatus of a third exemplary embodiment. 
         FIG. 11  is a diagram showing a configuration example of a control apparatus of the third exemplary embodiment. 
         FIG. 12  is an example of a database held by a policy DB of the control apparatus. 
         FIG. 13  is an example of a database held by the policy DB of the control apparatus. 
         FIG. 14  is an example of a database held by the policy DB of the control apparatus. 
         FIG. 15  is an example of a database held by the policy DB of the control apparatus. 
         FIG. 16  is a diagram showing a system configuration example of a fourth exemplary embodiment. 
         FIG. 17  is a diagram describing technology related to the fourth exemplary embodiment. 
         FIG. 18  is a diagram describing technology related to the fourth exemplary embodiment. 
         FIG. 19  is a diagram showing a configuration example of the communication apparatus of the fourth exemplary embodiment. 
         FIG. 20  is a diagram showing a configuration example of a packet forwarding function unit. 
         FIG. 21  is a diagram showing an example of information notified by the communication apparatus to the control apparatus. 
         FIG. 22  is a diagram showing a configuration example of the control apparatus of the fourth exemplary embodiment. 
         FIG. 23  is a diagram showing an example of a database held by the control apparatus. 
         FIG. 24  is a diagram showing an example of a packet processing rule generated by the control apparatus. 
         FIG. 25  is a sequence diagram showing an operation example of the fourth exemplary embodiment. 
         FIG. 26  is a diagram showing a system configuration example of a fifth exemplary embodiment. 
         FIG. 27  is a diagram showing an example of information managed by the control apparatus. 
         FIG. 28  is a diagram showing an example of an instruction notified by the control apparatus to the communication apparatus. 
         FIG. 29  is a diagram showing an example of an instruction notified by the control apparatus to a packet forwarding apparatus. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Exemplary Embodiment 
       FIG. 1  shows a configuration example of a system in a first exemplary embodiment. The system includes a communication apparatus  1 , a control apparatus  2 , a network  3 , and RATs  4 . It is to be noted that reference symbols in the drawing are added as examples in order to aid understanding, and are not intended to limit the present invention to modes shown in the drawings. Similarly, reference symbols in drawings related to other exemplary embodiments are also not intended to limit the present invention to modes shown in the drawings. 
     The communication apparatus  1  can communicate with a plurality of RATs (communication schemes). The communication apparatus  1  is connected with any of the RATs (RAT  4 - 1 , RAT  4 - 2 , RAT  4 - 3 , RAT  4 - 4 ) shown as examples in  FIG. 1 , to communicate with the network  3 . It is to be noted that the communication apparatus  1  (for example, wireless communication terminal) may be connected to a plurality of RATs (for example, RAT  4 - 1  and RAT  4 - 2 ), among the RATs shown as examples in  FIG. 1 , to communicate with the network  3 . 
     The communication apparatus  1  is an apparatus having a communication function such as, for example, a mobile telephone, a personal computer, a network switch, a router, a mobile router, or the like. It is to be noted that the mobile router, for example, is a terminal to relay a mobile telephone 3G line or a wireless LAN network. 
     RAT  4  is an access network for the communication apparatus  1  to connect with the network  3 . It is to be noted that RAT  4  includes access networks such as, for example, a UTRAN network, an LTE network, a WLAN network, WiMAX (Worldwide Interoperability for Microwave Access), and the like. 
       FIG. 2  shows an operation example in which the communication apparatus  1  establishes a link with a plurality of RATs, and obtains a plurality of communication addresses. 
     The communication apparatus  1  establishes a link with RAT  4 - 1 , and obtains a communication address (address (A)) corresponding to RAT  4 - 1 , from RAT  4 - 1 . The communication apparatus  1  executes communication by data packets with a communication partner (a), using the obtained communication address. 
     In a case where a link is established with RAT  4 - 2  while maintaining a link with RAT  4 - 1 , the communication apparatus  1  obtains a communication address (address (B)) from RAT  4 - 2 . As a result, the communication apparatus  1  obtains a plurality of communication addresses (address (A) and address (B)) from a plurality of RATs. 
     In a case of obtaining a plurality of communication addresses, for example, there is a possibility of it not being clear which of the plurality of communication addresses an application operating in the communication apparatus  1  should use. 
     The communication apparatus  1  is provided with a function to enable communication without determining which of the plurality of communication addresses should be used. 
       FIG. 3  shows a configuration example of the communication apparatus  1 . 
     The communication apparatus  1  includes a control unit  11  and communication interfaces  10 . 
     A communication interface  10 , for example, is an antenna or the like. The respective communication interfaces  10  correspond to at least one of the plurality of RATs. For example, a communication interface  10  corresponds to a certain RAT (for example, an UTRAN), and the communication apparatus  1  connects with a certain RAT (for example, an UTRAN) via the communication interface  10  in question. 
     Furthermore, for example, a communication interface  10  corresponds to a plurality of RATs (for example, RATs  4 - 2  and  4 - 3 ), and the communication apparatus  1  connects with any of the corresponding plurality of RATs via the communication interface  10  in question. In this case, the communication apparatus  1  may have a configuration having a single communication interface  10 . 
     The control unit  11  disguises a communication address corresponding to a certain communication scheme, based on an instruction from the control apparatus  2 , by a communication address corresponding to another communication scheme. The control unit  11  communicates with the control apparatus  2  and receives an instruction related to the disguise of the communication address. 
     The control unit  11  communicates with the control apparatus  2  via a communication interface. The control unit  11 , for example, refers to a network address of the control apparatus  2  that is set in advance in the communication apparatus  1 , and communicates with the control apparatus  2 . When the communication apparatus  1  connects with a RAT with which it is attempting to establish a link at startup or the like, being a communication line of a network operator to which the communication apparatus  1  is subscribed, the control unit  11  may obtain an address of the control apparatus  2  from the network side. For example, when a request to generate a logical channel (for example, a bearer) is made to a wireless station of a RAT for which a link is established, the control unit  11  also requests an address (IP (Internet Protocol) address or the like) of the control apparatus  2 . The control unit  11  may access the control apparatus  2  using a prescribed URL (Uniform Resource Locator), and may establish a VPN (Virtual Private Network) with the control apparatus  2 . It is to be noted that a method by which the control unit  11  communicates with the control apparatus  2  is not limited to the method described above. 
       FIG. 4  and  FIG. 5  show an outline of functions provided by the control unit  11 . It is to be noted that  FIG. 4  and  FIG. 5  are examples, and the functions of the control unit  11  are not limited to  FIG. 4  and  FIG. 5 . 
     The communication apparatus  1  obtains a communication address (A) from the RAT  4 - 1 , and obtains a communication address (B) from RAT  4 - 2 . 
     An application running on the communication apparatus  1  uses the communication address (A) to attempt communication with a communication partner in the network. The control unit  11  is instructed by the control apparatus  2  to communicate via the RAT  4 - 2 . 
     The control unit  11  disguises a communication address (A) by a communication address (B) corresponding to a RAT used in communication, based on an instruction from the control apparatus  2 . Since the control unit  11  disguises the address, the communication partner recognizes the address of the communication apparatus  1  as if it were the communication address (B). 
     Since the control unit  11  disguises an address based on an instruction of the control apparatus  2 , an application running on the communication apparatus  1  can commence communication by an arbitrary communication address, among a plurality of communication addresses set in the communication apparatus  1 . That is, the application need not determine a communication address used in communication. Accordingly, a maker of an application operated by the communication apparatus  1  need not add to the application a function for handling a case where a plurality of communication addresses are assigned to the communication apparatus  1 . 
     In a case where a communication address used by an application does not corresponding to a RAT used by the communication apparatus  1  in communication, if there is no function corresponding to the control unit  11 , there is a possibility of a failure occurring in communication. However, by the communication address being disguised by the control unit  11 , even in a case where a communication address used by an application does not correspond to a RAT used by the communication apparatus  1  in communication, the communication apparatus  1  is able to perform communication. 
     Since the address of the communication apparatus  1  is recognized as a communication address (B), as shown in  FIG. 5 , a communication partner transmits a response to the communication apparatus  1 , to a destination of the communication address (B). 
     The control unit  11  releases the disguise of the communication with the communication address (B). That is, the control unit  11  delivers the communication with the destination of the communication address (B) delivered from the communication partner to the application, as a communication with a destination of the communication address (A). 
     It is to be noted that the control unit  11  can also be configured by a software application. For example, the communication apparatus may download a software application having a function corresponding to the control unit  11 , from a server on the network. The server that delivers the software application to the communication apparatus  1 , for example, is provided with a function to communicate with the communication apparatus  1  via the network  3  of the communication system shown in  FIG. 1 , and to deliver a software application corresponding to the control unit  11 , to the communication apparatus  1 . 
     The control unit  11  may have a function to enable communication with the control apparatus  2 , without disguising the communication address. For example, the control unit  11  is provided with a function to select a communication address corresponding to a RAT used in communication with the control apparatus  2 . The RAT used in communication with the control apparatus  2  may be set in advance in the control unit  11 . 
       FIG. 6  shows an operation example in the first exemplary embodiment. 
     The communication apparatus  1  obtains a plurality of communication addresses from a plurality of RATs, in a sequence the same as the operation example shown in  FIG. 2 . 
     The control apparatus  2  determines a RAT to be used by the communication apparatus  1 . The control apparatus  2  transmits an instruction indicating that a communication address is to be disguised, based on the determined RAT, to the communication apparatus  1 . For example, the control apparatus  2  instructs the communication apparatus  1  to disguise the communication address to be used by an application, with a communication address corresponding to the determined RAT. 
     It is to be noted that timing at which the control apparatus  2  transmits an instruction to the communication apparatus  1  may be arbitrary. For example, the instruction may be transmitted in advance, before the communication apparatus  1  commences communication. For example, a request may be made for the instruction to the control apparatus  2  when the communication apparatus  1  commences communication, and the control apparatus  2  may transmit the instruction in response to the request. 
     The control unit  11  disguises a communication address, making reference to the instruction of the control apparatus  2 , and communicates with a communication partner. 
     Second Exemplary Embodiment 
     A system configuration example of a second exemplary embodiment is similar to  FIG. 1 . A configuration example of a communication apparatus  1  in the second exemplary embodiment is similar to  FIG. 3 . 
       FIG. 7  shows a configuration example of a control apparatus  2 . 
     The control apparatus  2  includes a communication unit  20 , a control unit  21 , and a management DB (Database)  23 . 
     The communication unit  20  has a function for communicating with the communication apparatus  1 . The control apparatus  2  transmits an instruction related to disguising a communication address to the communication apparatus  1 , via the communication unit  20 . 
     The control unit  21  makes reference to the management DB  23  and generates an instruction related to disguising a communication address. The control unit  21  builds a database of the management DB  23 , based on information notified from the communication apparatus  1 . 
       FIG. 8  shows an example of information notified by the communication apparatus  1  to the control apparatus  2 . The communication apparatus  1 , for example, notifies a communication scheme corresponding to an interface, an interface state (for example, whether or not a link is established with a communication network), and a communication address corresponding to the interface, to the control apparatus  2 . By the information being notified by the communication apparatus  1 , the control apparatus  2  recognizes a state of the communication apparatus  1  (for example, assigned communication address). 
       FIG. 9  shows an example of a database built by the control unit  21  in the management DB  23 . 
     The management DB  23  manages information notified by respective communication apparatuss  1 , for each communication apparatus  1 . The management DB  23  distinguishes a communication apparatus according to an ID of the communication apparatus  1 . The ID of the communication apparatus  1 , for example, is an IMSI (International Mobile Subscriber Identity) or the like. 
     The control unit  21  makes reference to the management DB  23  and generates an instruction related to a RAT (communication scheme) used by the communication apparatus  1 , and to disguising a communication address. The control unit  21 , for example, determines the RAT to be used by the communication apparatus  1 , from a RAT for which a link is established. The control unit  21 , for example, uses a communication address corresponding to the determined RAT to generate an instruction to disguise a communication address generated by the communication apparatus  1 . 
     Third Exemplary Embodiment 
     In a third exemplary embodiment, a control unit  11  of a communication apparatus carries out disguising with a communication address, by an instruction determined by the abovementioned control apparatus based on a status of the communication apparatus, which changes with movement of the communication apparatus. 
     A system configuration of the third exemplary embodiment is similar to  FIG. 1 . However, configurations of the communication apparatus and the control apparatus are different from the exemplary embodiments described above. In the third exemplary embodiment, the communication apparatus and the control apparatus are respectively described as the communication apparatus  1 A and the control apparatus  2 A. 
       FIG. 10  shows a configuration example of the communication apparatus  1 A in the third exemplary embodiment. The control unit  11  of the communication apparatus  1 A includes a monitor unit  111  and a notification unit  112 . The configuration is otherwise the same as the configuration example of  FIG. 2 . 
     The monitor unit  111  monitors status that changes in accordance with movement of the communication apparatus  1 A. The status which changes in accordance with movement is, for example, the location of the communication apparatus  1 A, a RAT that can be used by the communication apparatus  1 A, the radio wave reception intensity of each communication interface, or the like. 
     The monitor unit  111 , for example, searches for a RAT  4  that can be used in the vicinity of the communication apparatus  1 A, via the respective communication interfaces  10 . The monitor unit  111 , for example, searches for a useable RAT  4 , via all of the communication interfaces  10 . The monitor unit  111  may search for a useable RAT  4  via an interface that is running, among a plurality of communication interfaces. The monitor unit  111 , for example, searches for a useable RAT  4  based on radio wave conditions corresponding to respective RATs  4 . 
     The monitor unit  111  may measure information related to the location of the communication apparatus  1 A, or information related to radio wave conditions such as the radio wave reception intensity or the like, via a communication interface  10 . The information related to the location of the communication apparatus  1 A is, for example, GPS (Global Positioning System) information, cell ID (ID of a cell corresponding to a cover area of a wireless base station), or the like. 
     The notification unit  112  gives notification of information (referred to below as status information) related to status of the communication apparatus  1 A, monitored by the monitor unit  111 , to the control apparatus  2 A. The notification unit  112  gives notification of the status information to the control apparatus  2 A by a communication interface  10  corresponding to a RAT for which the communication apparatus  1 A establishes a link. The notification unit  112  may give notification of an identifier of the communication apparatus  1 A together with the status information, to the control apparatus  2 A. 
     It is to be noted that the notification unit  112  may have a function to enable communication with the control apparatus  2 A, without disguising a communication address. For example, the notification unit  112  is provided with a function to select a communication address corresponding to a RAT used in communication with the control apparatus  2 A. The RAT used in communication with the control apparatus  2 A may be set in advance in the notification unit  112 . 
     The notification unit  112 , for example, notifies the control apparatus  2 A of an identifier of a detected RAT or information related to radio wave conditions such as the reception field intensity, as status information. The RAT identifier is, for example, a SSID (Service Set Identifier) or a PLMN (Public Land Mobile Network) identifier. The notification unit  112  may give notification of information related to the location of the communication apparatus  1 A to the control apparatus  2 A as status information. The information related to the location of the communication apparatus  1 A is, for example, GPS information, cell ID (ID of a cell corresponding to a cover area of a wireless base station), or the like. 
     The control apparatus  2 A determines a RAT to be used by the communication apparatus  1 A, based on the status information notified by the communication apparatus  1 A. The control apparatus  2 A transmits an instruction to disguise a communication address, to the communication apparatus  1 A, according to a communication address corresponding to the determined RAT. 
     The control apparatus  2 A may determine a RAT to which the communication apparatus  1 A is connected, and may identify a connection apparatus (for example, a WiFi access point) in order to connect with the RAT. The control apparatus  2 A may instruct a communication apparatus  1 A to connect with a specified connection apparatus. The control apparatus  2 A, for example, gives notification of an SSID of a WiFi access point to the communication apparatus  1 A, and instructs that a connection be made to the access point of the SSID in question. 
     The monitor unit  111  monitors the state of the communication apparatus  1 A at prescribed timing. For example, the monitor unit  111  monitors the state of the communication apparatus  1 A at a prescribed period. The monitor unit  111  may monitor the state of the communication apparatus  1 A when instructed to do so by the control unit  11 . 
     The monitor unit  111  may monitor the amount of movement of the communication apparatus  1 A at regular intervals, and may monitor the status of a useable RAT or the like, only in a case where the amount of movement is greater than or equal to a prescribed threshold. If a monitoring operation such as scanning RAT information and the like is performed frequently, power consumption of the communication apparatus  1 A increases. However, in a case where the amount of movement of the communication apparatus  1 A is small, since the probability that the state of the communication apparatus  1 A has changed is low, there is little need to frequently execute a monitoring operation. Therefore, it is possible to curtail the power consumption of the communication apparatus  1 A by controlling the period and frequency of the monitor operation in accordance with the amount of movement of the communication apparatus  1 A. 
       FIG. 11  shows a configuration example of the control apparatus  2 A in the present exemplary embodiment. The control apparatus  2 A includes a communication unit  20 , a control unit  21 , a policy DB  22 , and a management DB  23 . A configuration example of a database stored in the management DB  23  is the same as in  FIG. 9 . 
     The communication unit  20  communicates with the communication apparatus  1 A. The communication unit  20 , for example, receives status information transmitted from the communication apparatus  1 A. The communication unit  20  transmits an instruction generated based on a RAT determined based on the received status information, to the communication apparatus  1 A. 
     The control unit  21  makes reference to the policy DB  22  to determine the RAT. That is, the control unit  21  makes reference to the status information received from the communication apparatus  1 A, to determine the RAT to which the communication apparatus  1 A connects. 
       FIG. 12  shows a configuration example of the policy DB  22 . It is to be noted that  FIG. 12  is an example, and the database held by the policy DB  22  is not limited to  FIG. 12 . 
     In  FIG. 12 , the policy DB  22  holds an identifier of a RAT for selection, for each RAT, as a rule (“selection rule” in the drawings) for determining the RAT. It is to be noted that the policy DB  22 , for example, holds data in a structure shown in  FIG. 12  for each communication apparatus  1 A. The policy DB  22 , for example, holds data in the structure shown in  FIG. 12  for each identifier (for example, IMSI (International Mobile Subscriber Identity), etc.) of a communication apparatus  1 A. 
     The control unit  21  makes reference to the status information received from the communication apparatus  1 A and the policy DB  22 , to determine a RAT to which the communication apparatus  1 A connects. The status information includes, for example, an identifier of a RAT detected by the communication apparatus  1 A. The identifier of the RAT, for example, is a PLMN (Public Land Mobile Network) identifier, which is identifier information of a UTRAN or the like. 
     The control unit  21 , for example, searches for data corresponding to the identifier of the communication apparatus  1 A that transmits status information, from the policy DB  22 . The control unit  21  compares the identifier of the RAT included in the received status information and the identifier specified in a selection rule of the policy DB  22 . In a case where an identifier included in the status information matches an identifier specified as a selection rule, the control unit  21  determines a RAT corresponding to the matching identifier as the RAT to which the communication apparatus  1 A connects. In the example of  FIG. 12 , in a case where the status information includes an SSID (A) that is an identifier of RAT  4 - 3  of  FIG. 1 , the control unit  21  instructs the communication apparatus  1 A to disguise communication using a communication address corresponding to the RAT  4 - 3 . 
     In a case where the status information includes information related to a radio wave condition such as field intensity or the like, the control unit  21  refers to the information to determine a RAT. In a case where an identifier included in the status information matches an identifier specified in a selection rule, for example, the control unit  21  selects an identifier with a good radio wave condition, among matching identifiers. 
     The policy DB  22  may have priorities.  FIG. 13  shows an example where the policy DB  22  has priorities. It is to be noted that  FIG. 13  is an example, and the database held by the policy DB  22  is not limited to  FIG. 13 . The policy DB  22 , for example, has priorities with respect to RAT (access scheme), and priorities for each selection rule of each RAT (that is, for each identifier of each RAT). The policy DB  22  holds a database of the structure of  FIG. 13  for each communication apparatus  1 A. 
     In a case where the status information received from the communication apparatus  1 A includes information related to a plurality of RATs, the control unit  21 , for example, refers to priorities for each RAT to select a RAT of high priority. 
     In a case where the status information includes a plurality of identifiers for a certain RAT, the control unit  21 , for example, refers to priorities for selection rules, and selects an access network corresponding to an identifier of high priority. 
     In the example of  FIG. 13 , in a case where the status information includes an identifier of an UTRAN and an identifier of a WLAN, the control unit  21  controls the communication apparatus  1 A so as to connect with a WLAN that has high priority. In a case where the status information includes an SSID (B) that is an identifier of RAT  4 - 2  and an SSID (A) that is an identifier of RAT  4 - 3 , the control unit instructs the communication apparatus  1 A to disguise communication with a communication address corresponding to the WLAN  4 - 3  that has high priority. 
     The control unit  21  may select a RAT according to type of communication flow.  FIG. 14  shows an example of a policy DB  22  in a case where the control unit  21  selects a RAT according to type of communication flow. It is to be noted that  FIG. 14  is an example, and the database held by the policy DB  22  is not limited to  FIG. 14 . 
     A communication flow, for example, indicates a communication matching a prescribed condition. For example, a sequence of packets transmitted from a certain transmission source A to a certain destination B belongs to the same communication flow. 
     With regard to the policy DB  22 , a RAT that is a candidate for selection is specified for each type of communication flow. It is to be noted that the policy DB  22  may specify a plurality of RATs that are selection candidates for respective types of communication flow, and may hold priorities for respective RATs. 
     In the example of  FIG. 14 , in a case of confirming from status information that a communication apparatus  1 A can connect with both a UTRAN and a WLAN, the control unit  21  controls the communication apparatus  1 A so as to communicate using the WLAN for Web communication, and to communicate using the UTRAN for VoIP (Voice over IP) communication. The policy DB  22 , for example, holds a database of the structure of  FIG. 14  for each communication apparatus  1 A. 
     The control unit  21  may select a RAT based on location information of the communication apparatus  1 A.  FIG. 15  shows an example of the policy DB  22  in a case where the control unit  21  selects a RAT based on location information. It is to be noted that  FIG. 15  is an example, and the database held by the policy DB  22  is not limited to  FIG. 15 . 
     The location information of  FIG. 15 , for example, is GPS information or a cell ID. In a case where the location information is GPS information, the location of the communication apparatus  1 A is, for example, latitude, longitude, altitude. In a case where the location is a cell ID, the location of the communication apparatus  1 A, for example, is estimated from the cell ID and the radio wave reception intensity measured by the communication apparatus  1 A for the cell ID in question. The control unit  21 , for example, estimates how far the communication apparatus  1 A is distant from the central part of the cell, by the radio wave reception intensity, to estimate the location of the communication apparatus  1 A. In the case of a cell ID, the location may be estimated using a plurality of cell IDs (a set of a plurality of cell IDs and radio wave reception intensity is also possible), rather than a single cell ID (a set of a single cell ID and radio wave reception intensity is also possible). The policy DB  22 , for example, holds a database of a structure of  FIG. 15  for each communication apparatus  1 A. 
     In the example of  FIG. 15 , the policy DB  22  has a database associating a RAT that is a candidate for connection by a communication apparatus  1 A, for each item of location information. For example, the policy DB  22  manages a RAT that is useable by the communication apparatus  1 A, for each item of location information. 
     For example, a WiFi access point is arranged at a prescribed location for each network operator. Therefore, by obtaining information related to the access point arrangement from the network operator in advance, the control apparatus  2 A can recognize a correspondence relationship between the location information and a RAT corresponding to the access point. The communication apparatus  1 A can use an access point of a network operator to which it is subscribed. Accordingly, by referring to information of the subscription between the communication apparatus  1 A and the network operator, and the arrangement of the access point of the network operator, the control apparatus  2 A can recognize a correspondence relationship between the location information and the useable RAT, and can build the policy DB  22  shown in  FIG. 15 . The control apparatus  2 A may obtain information related to the network operator to which the communication apparatus  1 A is subscribed, from the communication apparatus  1 A, or may obtain the information from the network operator. 
     The control unit  21  makes reference to the policy DB  22 , to identify a RAT corresponding to location information received from the communication apparatus  1 A. The control unit  21  determines a RAT to which the communication apparatus  1 A connects, from the RAT identified based on the location information. The control unit  21 , for example, may determine a RAT by a method described with reference to  FIG. 13  or  FIG. 14  (a method based on priority or communication flow), from the RAT identified based on the location information. 
     The control unit  21  can determine the RAT to which the communication apparatus  1 A connects, by any method described with reference to  FIG. 12 ,  FIG. 13 ,  FIG. 14 , and  FIG. 15 . The control unit  21  can determine the RAT by arbitrarily combining methods described with reference to  FIG. 12 ,  FIG. 13 ,  FIG. 14 , and  FIG. 15 . 
     As described above, by the control apparatus  2 A determining a RAT to which the communication apparatus  1 A connects based on the policy DB  22 , it is possible to easily select a RAT according to access environment of the communication apparatus  1 A. 
     By the control apparatus  2 A switching the RAT to which the communication apparatus  1 A connects in accordance with a communication flow, it is possible to control the network traffic of the communication apparatus  1 A by the network operator. By the network operator switching the RAT to which the communication apparatus  1 A connects, it is possible to disperse the network traffic of the communication apparatus  1 A to a plurality of RATs. In this way, the network operator can disperse communication volume which is continually increasing in recent years. 
     Fourth Exemplary Embodiment 
       FIG. 16  shows a system configuration example in a fourth exemplary embodiment. 
     The system of  FIG. 16  includes an LTE network  6  and a WLAN network  7 , as examples of RATs. 
     Configurations of a communication apparatus and a control apparatus are different from the exemplary embodiments described above. In the fourth exemplary embodiment, the communication apparatus and the control apparatus are respectively described as the communication apparatus  1 B and the control apparatus  2 B. 
     The communication apparatus  1 B communicates with a server apparatus  5 . 
     The fourth exemplary embodiment shows an example in which the present invention is implemented by improving technology known as OpenFlow, which is centrally controlled network architecture. 
     Referring to  FIG. 17  and  FIG. 18 , a description is given concerning OpenFlow technology. 
     OpenFlow recognizes communication as end-to-end flow, and executes path control, failure recovery, load balancing and the like on a per-flow basis.  FIG. 17  shows an outline of a communication system configured according to OpenFlow. It is to be noted that a flow is, for example, a group of a sequence of communication packets having a prescribed attribute. An OpenFlow switch  600  is a network switch that uses OpenFlow technology. An OpenFlow controller  700  is an information processing apparatus that controls the OpenFlow switch  600 . 
     The OpenFlow switch  600  communicates with the OpenFlow controller  700  via a secure channel  701  set between the OpenFlow controller  700  and the OpenFlow switch  600 . The OpenFlow controller  700  performs setting of a flow table  601  of the OpenFlow switch  600 , via the secure channel  701 . It is to be noted that the secure channel  701  is a communication path disposed in order to prevent wiretapping or falsification of communication between the OpenFlow switch  600  and the OpenFlow controller  700 . 
       FIG. 18  shows a configuration example of respective entries (flow entries) of the flow table  601 . A flow entry is configured by a matching rule for matching information (for example, destination IP address, VLAN ID, or the like) included in a header of a packet received from a switch, statistical information (Counters) that is statistical information of each packet flow, and actions (Actions) that prescribe a method of processing a packet matching a matching rule. 
     On receiving a packet, the OpenFlow switch  600  makes reference to the flow table  601 . The OpenFlow switch  600  searches for a flow entry that matches header information of a received packet. In a case where an entry that matches header information of the received packet is retrieved, the OpenFlow switch  600  processes the received packet in accordance with a processing method defined in an action field of the retrieved entry. The processing method, for example, defines “forward a received packet from a prescribed port,” “drop a received packet,” or “rewrite part of the header of a received packet and forward from a prescribed port.” 
     On the other hand, in a case where an entry matching the header information of the received packet is not found, the OpenFlow switch  600 , for example, forwards the received packet to the OpenFlow controller  700  via the secure channel  701 . By forwarding the received packet, the OpenFlow switch  600  makes a request for setting of a flow entry prescribing a processing method for the received packet, to the Open Flow controller  700 . It is to be noted that in a case where the received packet matches an entry prescribing that a request be made for setting of a flow entry to the OpenFlow controller  700 , the OpenFlow switch  600  may make a request for setting of the flow entry to the OpenFlow controller  700 . 
     The OpenFlow controller  700  determines a processing method for the received packet, and sets a flow entry including the determined processing method in the flow table  601 . Thereafter, the OpenFlow switch  600  processes subsequent packets belonging to the same flow as the received packet by the flow entry that has been set. 
       FIG. 19  shows a configuration example of the communication apparatus  1 B. The communication apparatus  1 B includes a function corresponding to the OpenFlow switch  600 . It is to be noted that functionality corresponding to the OpenFlow switch  600  may be either by hardware or software. 
     A packet forwarding function unit  103  includes a part of the functionality corresponding to the OpenFlow switch  600 . The packet forwarding function unit  103  has a plurality of port units  104 . In an example of  FIG. 19 , the packet forwarding function unit  103  has n (n is an integer) port units  104 . Respective communication interfaces  105 , for example, are associated with at least one of the plurality of port units  104 . The packet forwarding function unit  103  transmits/receives data via the port units  104 . 
     In the communication apparatus  1 B, a plurality of applications (application unit  101  # 1 -#N) are running. The applications generate packets, and communicate with the network  3  via a RAT (the LTE network  6  or the WLAN network  7 ) 
     When an application transmits a packet to the network  3 , the packet is processed by a protocol stack unit  102  (for example, a protocol stack of an OSI (Open Systems Interconnection) reference model or the like), and formed into a packet with a prescribed protocol stack attached. The packet is transmitted from a communication interface  105  via the packet forwarding function unit  103 . 
     The communication apparatus  1 B obtains a plurality of respective corresponding IP addresses from the plurality of RATs (for example, the LTE network  6  and the WLAN network  7 ). The IP address corresponding to the LTE network  6  is IP address (LTE), and the IP address corresponding to the WLAN network  7  is IP address (WLAN). 
     The application unit  101  and the protocol stack unit  102  generate packets using an arbitrary IP address, among a plurality of IP addresses assigned to the communication apparatus  1 B. For example, the application unit  101  and the protocol stack unit  102  generate packets using a first recognized address among the plurality of IP addresses. 
     The packet forwarding function unit  103  transmits packets from the port unit  104 , in accordance with a packet processing rule (for example, a flow entry) set by the control apparatus  2 B. Packets forwarded by the port unit  104  are transmitted via any of the communication interfaces  105 , to an access network of a RAT corresponding to the interface in question. A packet received from the access network of the RAT by the communication interface  105  is sent to an application via the port unit  103 . 
     The packet forwarding function unit  103  is provided with a function for disguising an IP address used by the application unit  101  and the protocol stack unit  102 , by another IP address corresponding to a RAT used by the communication apparatus  1 B, in accordance with a packet processing rule set by the control apparatus  2 B. The packet forwarding function unit  103  is provided with a function for releasing the disguise of a packet transmitted to the communication apparatus  1 B, using an IP address corresponding to the RAT used by the communication apparatus  1 B. In a case where the application unit  101  and the protocol stack unit  102  use an IP address corresponding to the RAT used by the communication apparatus  1 B, the packet forwarding function unit  103  need not disguise the IP address of the packet. 
       FIG. 20  is a configuration example of the packet forwarding function unit  103 . 
     The communication unit  130  communicates with the control apparatus  2 B. The communication unit  130 , for example, sets a secure channel  701  between itself and the control apparatus  2 B, in order that the packet forwarding function unit  103  receives a packet processing rule transmitted from the control apparatus  2 B. The control unit  130 , for example, makes a request for a packet processing rule to the control apparatus  2 B, via the secure channel  701  that has been set. 
     The communication unit  130  delivers the packet processing rule received from the control apparatus  2 B to the processing rule management unit  134 . The processing rule management unit  134  stores the packet processing rule received from the control apparatus  2 B in a processing rule DB  135 . 
     A processing unit  131  executes processing such as packet forwarding or rewriting of a packet header portion, in accordance with a packet processing rule set by the control apparatus  2 B. A retrieval unit  136  retrieves a packet processing rule matching a packet, among packet processing rules stored in the processing rule DB  135 . The retrieval unit  136 , for example, collates packet content and a matching rule of the packet processing rule, and retrieves a processing rule including the matching rule that matches the packet content. In a case where a processing rule matching the packet is not stored in the processing rule DB  135 , the retrieval unit  136 , for example, notifies the communication unit  130  and the communication unit  130  makes a request for a packet processing rule to the control apparatus  2 B. It is to be noted that a configuration of the packet processing rule may be the same as the configuration shown in  FIG. 18 . 
     An action execution unit  137  processes the packet in accordance with a processing rule specified in the packet processing rule retrieved by the retrieval unit  136 . For example, the action execution unit  137  executes processing in which the packet is forwarded from a prescribed port unit  104 , processing in which the packet content is rewritten, or the like. 
     The action execution unit  137  disguises an IP address in accordance with a packet processing rule. That is, the action execution unit  137  disguises the IP address of a communication flow corresponding to a packet processing rule retrieved by the retrieval unit  136 . 
     An IF (Interface) management unit  132  manages information related to a communication interface  105 , using an IP management DB  133 . The IF management DB  133 , for example, has a database as exemplified in  FIG. 21 . The database, for example, holds the number of the corresponding port unit  104 , a corresponding communication scheme, the state of a link between the communication interface  105  and a RAT, and addresses corresponding to the communication interface  105  (for example, a MAC (Media Access Control) address and an IP address), for each communication interface  105 . 
     In a case where a correspondence relationship between the communication interface  105  and the port unit  104  is changed, the IF management unit  132  updates the IF management DB  133 . 
     The IF management unit  132  gives notification of at least some of the information managed by the IF management DB  133  to the control apparatus  2 B, via the communication unit  130 . The control apparatus  2 B recognizes the state of the communication apparatus  1 B, by receiving this information. In a case of receiving a request from the control apparatus  2 B, for example, the IF management unit  132  gives notification of this information. 
     In a case where the communication interface used is switched in accordance with an instruction from the control apparatus  2 B, the IF management unit  132  changes the port unit used by the packet forwarding function unit  103 . In a case where the port unit used by the packet forwarding function unit  103  is changed accompanying switching of the communication interface, the IF management unit  132  updates the IF management DB  133 . It is to be noted that the IF management DB  133  may manage a correspondence relationship between a contact point (for example, an access point) of a RAT to which the communication interface is connected, and the port unit. 
     The OpenFlow technology described above has a function (Port Status) by which the state of a port of a switch is notified to a controller, and a function (Feature Request/Reply) by which a feature of a switch is notified to the controller. The IF management unit  132  may use these functions when giving notification of information to the control apparatus  2 B. 
     The communication apparatus  1 B may be provided with a function for downloading a software module having a function equivalent to the packet forwarding function unit  103 . The communication apparatus  1 B may use the downloaded software module as the packet forwarding function unit  103 . 
       FIG. 22  shows a configuration example of the control apparatus  2 B. 
     The processing rule DB  208  stores a packet processing rule for setting in the communication apparatus  1 B. It is to be noted that a configuration of the packet processing rule may be the same as the configuration shown in  FIG. 18 . 
     A node communication unit  201  communicates with the communication apparatus  1 B. The node communication unit  201  forwards information received from the communication apparatus  1 B to a packet forwarding function management unit  209 . 
     The packet forwarding function management unit  209  manages information (for example, the information exemplified in  FIG. 21 ) transmitted from the IF management unit  132  of the communication apparatus  1 B. The control apparatus  2 B recognizes the state of the communication apparatus  1 B, by the packet forwarding function management unit  209 . 
     The packet forwarding function management unit  209  manages information notified by communication apparatus for each communication apparatus  1 B. The packet forwarding function management unit  209 , for example, manages information by a database as exemplified in  FIG. 23 . 
     A calculation unit  203  determines packet processing to be executed in a packet forwarding path and a switch in the forwarding path, based on network topology. That is, the calculation unit  203  calculates a packet forwarding path, and determines a packet processing rule corresponding to the forwarding path. 
     The calculation unit  203  refers to information managed by the packet forwarding function management unit  209  and determines a processing rule for disguising an IP address. The calculation unit  203 , for example, transmits a packet processing rule as exemplified in  FIG. 24 , to the communication apparatus  1 B. The control apparatus  2 B, for example, determines a RAT to be used by the communication apparatus  1 B, by a method as in the third exemplary embodiment. The calculation unit  203  determines a packet processing rule prescribing disguising of communication using an address corresponding to a RAT used by the communication apparatus  1 B. In a case where a RAT used by the communication apparatus  1 B is determined to be a WLAN, the calculation unit  203 , as in an example of  FIG. 24 , determines a packet processing rule that converts a transmission source IP address to an IP address corresponding to the WLAN network, for a communication flow where the transmission source IP address is an IP address corresponding to an LTE network. The calculation unit  203 , as in the example of  FIG. 24 , determines a packet processing rule that converts a destination IP address to an IP address corresponding to the LTE network, for a communication flow where the IP address corresponding to a WLAN network is the destination. The calculation unit  203  instructs the communication apparatus  1 B to disguise communication, by the packet processing rule described above. 
     The DB management unit  207  records the packet processing rule determined by the calculation unit  203  in the processing rule DB  208 . The DB management unit  207  transmits a packet processing rule to the communication apparatus  1 B, in response to a request for a packet processing rule being transmitted from the communication apparatus  1 B. 
     A control message processing unit  202  analyzes a control message (for example, a request to set a packet processing rule, or the like) received from the communication apparatus  1 B, and performs processing corresponding to the control message. The control message processing unit  202  generates a message (for example, a message for setting a packet processing rule, or the like) to be transmitted to the communication apparatus  1 B. 
       FIG. 25  is a sequence diagram showing an operation example of the fourth exemplary embodiment. 
     The communication apparatus  1 B establishes links with each of the LTE network  6  and the WLAN network  7 . The communication apparatus  1 B obtains IP addresses from each of the LTE network  6  and the WLAN network  7 . 
     The packet forwarding function unit  103  sets a control channel between itself and the control apparatus  2 B, via any RAT in which a link is established. The packet forwarding function unit  103  communicates with the control apparatus  2 B, via the control channel. The control channel, for example, is the secure channel  701  of the OpenFlow technology described above. 
     The control apparatus  2 B makes a request to the communication apparatus  1 B for transmission of information related to a feature of the communication apparatus  1 B, via the control channel (Feature Request). 
     The packet forwarding function unit  103  gives notification of information to the control apparatus  2 B, in response to the request from the control apparatus  2 B. The packet forwarding function unit  103  may notify the control apparatus  2 B of information exemplified in  FIG. 21 , by using a “Feature Reply” function. 
     In a case of receiving a packet for which a corresponding processing rule is unknown, or a case of receiving a packet corresponding to a processing rule prescribing an enquiry to the control apparatus, the packet forwarding function unit  203  makes a request for a packet processing rule to the control apparatus  2 B, at a prescribed timing. 
     The control apparatus  2 B determines a packet processing rule in response to the request from the packet forwarding function unit  203  and transmits the packet processing rule to the communication apparatus  1 B. The control apparatus  2 B determines a RAT to be used by the communication apparatus  1 B. The control apparatus  2 B makes reference to information (an IP address assigned to the communication apparatus  1 B) notified by the packet forwarding function unit  203 , and notifies the packet forwarding function unit  203  of an instruction to disguise an address corresponding to a RAT to be used by the communication apparatus  1 B. 
     The communication apparatus  1 B communicates with a server apparatus  5  that is a communication partner, based on the instruction transmitted from the control apparatus  2 B. 
     Fifth Exemplary Embodiment 
       FIG. 26  shows an example of a system configuration example in a fifth exemplary embodiment. 
     In the fifth exemplary embodiment, a network  3  includes a packet forwarding apparatus  4 . The fifth exemplary embodiment is otherwise the same as the fourth exemplary embodiment. 
     The packet forwarding apparatus  4  releases a disguise of a packet transmitted from a communication apparatus  1 B. By the packet forwarding apparatus  4  releasing the disguise, a communication address used by an application of the communication apparatus  1 B and a communication address recognized as an identifier of the communication apparatus  1 B by a communication partner are the same. Therefore, in the fifth exemplary embodiment, even where the communication apparatus  1 B performs handover between different RATs, it is not necessary to change a communication address of the communication apparatus  1 B, and it is possible to avoid a communication interruption (session disconnection) due to the handover. 
     The packet forwarding function management unit  209  of the control apparatus  2 B manages information shown in  FIG. 27 . Note that  FIG. 27  is an example, and the information managed by the packet forwarding function management unit  209  is not limited to  FIG. 27 . 
     The control apparatus  2 B generates an instruction to be transmitted to a packet forwarding function unit  103  and the packet forwarding apparatus  4  of the communication apparatus  1 B, based on information managed by the packet forwarding function management unit  209 . 
     The packet forwarding function management unit  209  manages the state of each port and a communication address (for example, a MAC address or an IP address) corresponding to each port, for each port number of the packet forwarding apparatus  4  and the communication apparatus  1 B. 
     A calculation unit  203  of the control apparatus  2 B transmits an instruction to disguise communication, to the communication apparatus  1 B, based on information managed by the packet forwarding function management unit  209 . The calculation unit  203  transmits an instruction to release the disguise by the communication apparatus  1 B, based on information managed by the packet forwarding function management unit  209 , to the packet forwarding apparatus  4 . 
     Making reference to  FIG. 28  and  FIG. 29 , a description is given of an example of operation of the communication apparatus  1 B and the packet forwarding apparatus  4 , according to an instruction of the control apparatus  2 B.  FIG. 28  shows an example of an instruction notified to the communication apparatus  1 B from the control apparatus  2 B.  FIG. 29  shows an example of an instruction notified to the packet forwarding apparatus  4  from the control apparatus  2 B. 
     The packet forwarding function unit  103  of the communication apparatus  1 B disguises a communication address used as an identifier of the communication apparatus  1 B, by a communication address instructed by the control apparatus  2 B. In an example of  FIG. 28  (first line of the table of  FIG. 28 ), in a case of using an address (IP address (LTE)) corresponding to an LTE network  6  as a communication address of an identifier of the communication apparatus  1 B, the packet forwarding function unit  103  converts the address to an address (IP address (WLAN)) corresponding to a WLAN network  7 . It is to be noted that the packet forwarding function unit  103  may convert a MAC address of a packet transmission source to a MAC address (MAC address (WLAN)) corresponding to the WLAN network  7 . 
     The packet forwarding function unit  103  converts the destination of a packet whose transmission source address is disguised, to an address of the packet forwarding apparatus  4 . The packet forwarding function unit  103 , for the packet whose destination address was converted, forwards a packet from a port unit  104  corresponding to a forwarding path to the packet forwarding apparatus  4 . 
     The packet forwarding apparatus  4  that receives a packet from the communication apparatus  1 B releases an address disguise. In an example of  FIG. 29  (first line of the table of  FIG. 29 ), in a case where the packet forwarding apparatus  4  receives a packet with a destination of the packet forwarding apparatus  4 , with a transmission source address being an address (IP address (WLAN)) for a WLAN of the communication apparatus  1 B, the packet forwarding apparatus  4  converts the packet transmission source address to an address (IP address (LTE)) for LTE of the communication apparatus  1 B. It is to be noted that the packet forwarding apparatus  4  may convert a MAC address of the packet transmission source to a MAC address (MAC address (LTE)) for LTE of the communication apparatus  1 B. 
     The packet forwarding apparatus  4  converts the packet destination address to an address of a server apparatus  5 . The packet forwarding apparatus  4  forwards the packet whose destination address was converted, from a port corresponding to a forwarding path to the server apparatus  5 . 
     The server apparatus  5  that receives the packet via the packet forwarding apparatus  4 , which was transmitted from the communication apparatus  1 B, transmits a reply packet with a destination of the communication apparatus  1 B. By the packet forwarding apparatus  4  releasing the packet disguise, the server apparatus  5  recognizes that the address of the communication apparatus  1 B is an address (IP address (LTE)) for LTE, from the transmission source address of the received packet. Therefore, the server apparatus  5  sets the destination of the reply packet to an LTE address (IP address (LTE)) of the communication apparatus  1 B. 
     It is to be noted that in the present exemplary embodiment, with regard to the network  3 , a packet with a destination of the communication apparatus  1 B is set so as to pass via the packet forwarding apparatus  4 . Therefore, the reply packet transmitted by the server apparatus  5  goes via the packet forwarding apparatus  4 . 
     The packet forwarding apparatus  4  receives the packet with a destination of the communication apparatus  1 B, that was transmitted by the server apparatus  5 . The destination of the packet is an LTE address of the communication apparatus  1 B, and the transmission source is the server apparatus  5 . Therefore, the packet forwarding apparatus  4  converts the destination address of the packet to a WLAN address of the communication apparatus  1 B, in accordance with the example of  FIG. 29  (second line of the table of  FIG. 29 ). The packet forwarding apparatus  4  forwards the packet whose destination address was converted, from a port corresponding to a forwarding path to the communication apparatus  1 B. 
     In a case of receiving a packet with a transmission source of the server apparatus  5 , and a destination of a WLAN address of the communication apparatus  1 B, the packet forwarding function unit  103  of the communication apparatus  1 B converts the packet address in accordance with the example of  FIG. 28  (second line of the table of  FIG. 28 ). The packet forwarding function unit  103  converts the destination of the received packet to an LTE address of the communication apparatus  1 B, and transmits the packet to a protocol stack unit  102 . 
     By the above operations, communication between the communication apparatus  1 B and the server apparatus  5  is executed via the packet forwarding apparatus  4 . 
     The entire disclosures of the above Patent Literatures are incorporated herein by reference thereto. Modifications and adjustments of the exemplary embodiment are possible within the scope of the overall disclosure (including the claims) of the present invention and based on the basic technical concept of the present invention. Various combinations and selections of various disclosed elements (including each element of each claim, each element of each exemplary embodiment, each element of each drawing, etc.) are possible within the scope of the claims of the present invention. That is, the present invention of course includes various variations and modifications that could be made by those skilled in the art according to the overall disclosure including the claims and the technical concept. Particularly, any numerical range disclosed herein should be interpreted that any intermediate values or subranges falling within the disclosed range are also concretely disclosed even without specific recital thereof. 
     Note that the term “means” used herein is interchangeable with the term “unit,” and vice versa. Note further that the singular form disclosed herein may also represent the plural form, as is relevant in the art, and particularly based on the priority text which is in Japanese language having inherently no difference between the singular form and the plural form. 
     REFERENCE SIGNS LIST 
     
         
           1  communication apparatus 
           1 B communication apparatus 
           2  control apparatus 
           2 B control apparatus 
           3  network 
           4  RAT 
           5  server apparatus 
           6  LTE network 
           7  WLAN network 
           10  communication interface 
           11  control unit 
           20  communication unit 
           21  control unit 
           22  policy DB 
           23  management DB 
           101  application unit 
           102  protocol stack unit 
           103  packet forwarding function unit 
           104  port unit 
           105  communication interface 
           111  monitor unit 
           112  notification unit 
           130  communication unit 
           131  processing unit 
           132  IF management unit 
           133  IF management DB 
           134  processing rule management unit 
           135  processing rule DB 
           136  retrieval unit 
           137  action execution unit 
           201  node communication unit 
           202  control message processing unit 
           203  calculation unit 
           207  DB management unit 
           208  processing rule DB 
           209  packet forwarding function management unit 
           600  OpenFlow switch 
           601  flow table 
           700  OpenFlow controller 
           701  secure chanel