Patent Publication Number: US-11659096-B2

Title: Gateway device, radio communication device, charging control method, data transmission method, and non-transitory computer readable medium

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is continuation of U.S. patent application Ser. No. 16/935,414, entitled “Gateway Device, Radio Communication Device, Charging Control Method, Data Transmission Method, And Non-Transitory Computer Readable Medium”, filed on Jul. 22, 2020, which is a continuation of U.S. patent application Ser. No. 16/251,628, entitled “Gateway Device, Radio Communication Device, Charging Control Method, Data Transmission Method, And Non-Transitory Computer Readable Medium”, filed on Jan. 18, 2019, now U.S. Pat. No. 10,764,443, which is a continuation of U.S. patent application Ser. No. 15/759,115, entitled “Gateway Device, Radio Communication Device, Charging Control Method, Data Transmission Method, and Non-Transitory Computer Readable Medium,” filed on Mar. 9, 2018, which is a 371 national stage of International Application No. PCT/JP2016/003998, filed on Sep. 1, 2016, which claims priority to Japanese Patent Application No. 2015-180484, filed on Sep. 14, 2015, the disclosures of which are hereby incorporated by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a gateway device, a radio communication device, a charging control method, a data transmission method, and a program and, particularly, relates to a gateway device, a radio communication device, a charging control method, a data transmission method, and a program using a plurality of radio access technologies. 
     BACKGROUND ART 
     3GPP (3rd Generation Partnership Project), a standard specification for mobile communication systems, introduces dual connectivity as a technique for a communication terminal UE (User Equipment) to carry out wideband and low-delay communications. The dual connectivity is a technique that allows a UE to have dual connections to a first base station MeNB (Master evolved NodeB) and a second base station SeNB (Secondary eNB) that perform LTE (Long Term Evolution) communications, for example, so that the UE communicates not only with the MeNB but also with the SeNB. This improves the throughput of communications. 
     Non Patent Literature 1 describes, as a dual connectivity procedure, a process flow or the like where a UE newly adds an SeNB as an eNB to communicate with the UE when the UE is being connected with an MeNB. 
     On the other hand, areas where wireless LAN (Local Area Network) communications, which enable high-speed communications although the coverage area is smaller than mobile communication systems, are available have been expanded recently. Thus, a technique where a UE connects to both an eNB that performs mobile communications and an access point WT (Wireless LAN Termination) that performs wireless LAN communications by applying the dual connectivity technology, and the UE communicates not only with the eNB but also with the WT (which is referred to hereinafter as LTE-WT aggregation, which may also be referred to as LTE-WT dual connectivity), has also been studied. To be more specific, the background, object and the like of this study are described in Non Patent Literature 2. 
     Note that a charging rate to be applied to a UE is determined on the basis of a radio access technology (RAT) being used by the UE. For example, when a UE is performing LTE communications with an MeNB and an SeNB in dual connectivity, a charging rate determined at the time of LTE communications is applied to the UE. Non Patent Literature 3 describes a PCC (Policy and Charging Control) architecture for carrying out policy control and charging control. 
     Non Patent Literature 4 describes that a gateway device PGW (Packet Date Network Gateway) manages RAT types on a UE-by-UE basis as parameters related to charging. The RAT type is a parameter indicating a RAT that is currently used by a UE. 
     CITATION LIST 
     Non Patent Literature 
     
         
         NPL1: 3GPP TS 36.300 V13.0.0 (2015-06) Section 10.1.2.8 
         NPL2: 3GPP TSG RAN Meeting #67 (2015-03) RP-150510 
         NPL3: 3GPP TS 23.203 V13.4.0 (2015-06) Section 5, Section A.4.2 
         NPL4: 3GPP TS 23.401 V13.1.0 (2014-12) Section 5.7.4 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     In the case of executing the dual connectivity described in Non Patent Literature 1, a UE performs communications with an MeNB and an SeNB simultaneously by using one RAT. In this case, no problem arises when RAT types as charging parameters are managed on a UE-by-UE basis as described in Non Patent Literature 4. However, in the case where a UE performs LTE-WT aggregation as described in Non Patent Literature 2, the UE performs communications using two types of RATs at the same time. Therefore, if a PGW manages RAT types on a UE-by-UE basis as described in Non Patent Literature 4, there is a possibility that a RAT type that is managed by the PGW and a RAT that is actually used by the UE could be different. This causes a problem that, when a UE performs communications using two types of RATs, it is not possible to conduct adequate charging control (apply a charging rate) in accordance with actual communications. 
     An exemplary object of the present invention is to provide a gateway device, a radio communication device, a charging control method, a data transmission method, and a program that achieve charging control in accordance with a RAT being used by a UE even when the UE is performing communications using different RATs at the same time. 
     Solution to Problem 
     A gateway device according to a first exemplary aspect of the present invention includes a management unit configured to, when a communication terminal forms communication aggregation by performing a first radio communication using a first radio access technology and a second radio communication using a second radio access technology, manage at least one bearer assigned to the communication terminal in association with information indicating the first and second radio access technologies, and a charging system communication unit configured to transmit the information indicating the first and second radio access technologies to at least one charging control device that performs charging control. 
     A radio communication device according to a second exemplary aspect of the present invention is a radio communication device that performs a first radio communication using a first radio access technology with a communication terminal, wherein, when the communication terminal forms communication aggregation by performing the first radio communication and a second radio communication using a second radio access technology, the radio communication device transmits information associating at least one bearer assigned to the communication terminal and information indicating the first and second radio access technologies to a network device that manages the bearer. 
     A charging control method according to a third exemplary aspect of the present invention includes, when a communication terminal forms communication aggregation by performing a first radio communication using a first radio access technology and a second radio communication using a second radio access technology, managing at least one bearer assigned to the communication terminal in association with information indicating the first and second radio access technologies, and transmitting the information indicating the first and second radio access technologies to at least one charging control device that performs charging control. 
     A data transmission method according to a fourth exemplary aspect of the present invention is a data transmission method used in a radio communication device that performs a first radio communication using a first radio access technology with a communication terminal, the method including, when the communication terminal forms communication aggregation by performing the first radio communication and a second radio communication using a second radio access technology, transmitting information associating at least one bearer assigned to the communication terminal and information indicating the first and second radio access technologies to a network device that manages the bearer. 
     A program according to a fifth exemplary aspect of the present invention causes a computer to execute, when a communication terminal forms communication aggregation by performing a first radio communication using a first radio access technology and a second radio communication using a second radio access technology, managing at least one bearer assigned to the communication terminal in association with information indicating the first and second radio access technologies, and transmitting the information indicating the first and second radio access technologies to at least one charging control device that performs charging control. 
     Advantageous Effects of Invention 
     According to the exemplary aspects of the present invention, it is possible to provide a gateway device, a radio communication device, a charging control method, a data transmission method, and a program that achieve charging control in accordance with a RAT being used by a UE even when the UE is performing communications using different RATs at the same time. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a schematic diagram of a communication system according to a first embodiment. 
         FIG.  2    is a schematic diagram of a communication system according to a second embodiment. 
         FIG.  3    is a schematic diagram of a charging system according to the second embodiment. 
         FIG.  4    is a schematic diagram of a PGW according to the second embodiment. 
         FIG.  5    is a view showing parameters managed by the PGW according to the second embodiment. 
         FIG.  6    is a schematic diagram of an eNB according to the second embodiment. 
         FIG.  7    is a schematic diagram of a UE according to the second embodiment. 
         FIG.  8    is a view showing a process flow of transmitting of a RAT type according to the second embodiment. 
         FIG.  9    is a view showing parameter information set to an E-RAB Modification Indication message according to the second embodiment. 
         FIG.  10    is a view showing parameter information set to a Modify Bearer Request message according to the second embodiment. 
         FIG.  11    is a view showing parameter information set to a Create Session Request message according to the second embodiment. 
         FIG.  12    is a view showing parameter information set to a Bearer Resource Command message according to the second embodiment. 
         FIG.  13    is a view showing parameter information set to a Modify Access Bearers Request message according to the second embodiment. 
         FIG.  14    is a view showing parameter information set to a Context Request message according to the second embodiment. 
         FIG.  15    is a view showing parameter information set to a Change Notification Request message according to the second embodiment. 
         FIG.  16    is a view showing a process flow of transmitting of a RAT type from a PGW to a PCRF according to the second embodiment. 
         FIG.  17    is a view showing a process flow of transmitting of a Diameter message between a PCRF and a TDF according to the second embodiment. 
         FIG.  18    is a view to explain values of RAT types according to the second embodiment. 
         FIG.  19    is a schematic diagram of a communication system according to a third embodiment. 
         FIG.  20    is a view to explain values of RAT types according to the third embodiment. 
         FIG.  21    is a view to explain values of RAT types according to the third embodiment. 
         FIG.  22    is a view showing parameter information set to an E-RAB Modification Indication message according to the third embodiment. 
         FIG.  23    is a schematic diagram of an eNB in each embodiment. 
         FIG.  24    is a schematic diagram of a UE in each embodiment. 
         FIG.  25    is a schematic diagram of a PGW in each embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     Embodiments of the present invention are described hereinafter with reference to the drawings. A configuration example of a communication system according to a first embodiment of the present invention is described with reference to  FIG.  1   . 
     The communication system in  FIG.  1    includes a communication terminal  10 , a radio communication device  21 , a radio communication device  22 , a gateway device  30 , and a policy charging control device  40 . 
     The communication terminal  10  may be a mobile phone terminal, a smartphone, a tablet terminal or the like. Further, the communication terminal  10  may be a UE, which is used as a general term for communication terminals in the 3GPP. Furthermore, the communication terminal  10  may be a terminal that performs communications using a 2G (2nd Generation mobile phone) radio access technology, a 3G (3rd Generation mobile phone) radio access technology, an LTE radio access technology, a 4G/5G (4th/5th mobile phone) radio access technology, or a radio access technology dedicated to supporting CIoT (Cellular IoT (Internet of Things)). Further, the communication terminal  10  is a terminal capable of performing simultaneous communications (dual connections) using a plurality of different radio access technologies. For example, the communication terminal  10  may be a terminal that performs a mobile communication using a radio access technology specified in the 3GPP and a wireless LAN communication at the same time. Further, the communication terminal  10  may be a terminal that performs the LTE radio access technology and the 5G radio access technology at the same time. 
     The radio communication device  21  and the radio communication device  22  perform radio communications with the communication terminal  10  by using a predetermined radio access technology (RAT). The communication terminal  10  performs radio communications with the radio communication device  22  by using a RAT different from a RAT used for radio communications with the radio communication device  21 . A feature where the communication terminal  10  performs radio communications with the radio communication device  21  and the radio communication device  22  by using different RATs at the same time is called communication aggregation, hybrid dual connectivity or the like. 
     One RAT used in the communication aggregation may be LTE whose communication specifications are defined in the 3GPP, or a radio communication technology whose communication specifications will be defined in the 3GPP in the future. This radio communication technology may be called 5G or the like, for example. The other RAT used in the communication aggregation may be wireless LAN. 
     The policy charging control device  40  is a device that performs control regarding a service policy and charging related processing related to the communication terminal  10 . 
     The gateway device  30  is a gateway device that is used when the communication terminal  10  communicates with a network including the radio communication device  21  and the radio communication device  22 , a network where a service is provided, or a different external network. Further, the gateway device  30  transmits charging parameters related to the communication terminal  10  to the policy charging control device  40 . 
     A configuration example of the gateway device  30  is described hereinafter. The gateway device  30  may be a computer device that operates when a processor executes a program stored in a memory. 
     The gateway device  30  includes a management unit  31  and a charging system communication unit (note that the communication unit is, in other words, a transmitting and receiving unit)  32 . The elements that constitute the gateway device  30  including the management unit  31 , the charging system communication unit  32  and the like may be software, a module or the like whose processing is executed by running, on a processor, a program stored in a memory. Further, the elements that constitute the gateway device  30  may be software such as a circuit or a chip. 
     When the communication terminal  10  performs radio communications with the radio communication device  21  and the radio communication device  22  and forms the communication aggregation, the management unit  31  manages at least one bearer assigned to the communication terminal  10  and information indicating a RAT to be used for communications with the radio communication device  21  and a RAT to be used for communications with the radio communication device  22  in association with each other. For example, in the case where a bearer that is assigned to enable the communication terminal  10  to perform a communication through the radio communication device  21  and a bearer that is assigned to enable the communication terminal  10  to perform a communication through the radio communication device  22  are different, the management unit  31  manages a bearer and a RAT in one-to-one association. 
     Alternatively, in the case where one bearer is assigned to the communication terminal  10 , and a RAT to be used for communications with the radio communication device  21  and a RAT to be used for communications with the radio communication device  22  are contained in one bearer, the management unit  31  manages two RATs in association with one bearer. Note that three or more RATs may be associated with one bearer. 
     The charging system communication unit  32  transmits, to the policy charging control device  40 , information regarding RATs that are managed on a bearer-by-bearer basis in the management unit  31 . 
     As described above, the gateway device  30  manages the RAT being used by the communication terminal  10  in association with each bearer and thereby notifies the policy charging control device  40  of the RAT being used by the communication terminal  10  on a bearer-by-bearer basis. The policy charging control device  40  can thereby accurately grasp the RAT actually used by the communication terminal  10  and perform charging control in accordance with the RAT. 
     Second Embodiment 
     A configuration example of a communication system according to a second embodiment of the present invention is described with reference to  FIG.  2   . In  FIG.  2   , a configuration example of a communication system that is composed of nodes defined in the 3GPP is described. Note that, in  FIG.  2   , illustration of a charging system is omitted, and the charging system is described later with reference to  FIG.  3   . 
     The communication system in  FIG.  2    includes a UE  50 , an eNB  60 , which is a base station for LTE, a 5G base station  70 , which is a base station for 5G, a mobility management node MME (Mobility Management Entity)  80 , a SGW (Serving Gateway)  90 , a PGW  100 , and a PCRF (Policy Control and Charging Rules) entity  110  (which is referred to hereinafter as PCRF  110 ). 
     The UE  50  corresponds to the communication terminal  10  in  FIG.  1   . The eNB  60  corresponds to the radio communication device  21  in  FIG.  1   . The 5G base station  70  corresponds to the radio communication device  22  in  FIG.  1   . The PGW  100  corresponds to the gateway device  30  in  FIG.  1   . The PCRF  110  corresponds to the policy charging control device  40  in  FIG.  1   . 
     The 5G base station  70  is a base station that supports 5G radio communications, which are next-generation radio communications to be defined in the 3GPP in the future. Although the next-generation radio communication technology or radio access technology is called 5G for the sake of making the explanation easier, it is not limited to being named 5G. Further, the UE  50  is a terminal that supports both the LTE and the 5G radio communications. 
     The MME  80  is a device that mainly gives a request or an instruction for mobility management and bearer setting of the UE  50 , or a request or an instruction for removal of a bearer. The SGW  90  and the PGW  100  are gateway devices that relay user data (packets) transmitted or received by the UE  50 . The SGW  90  accommodates a radio access system, and the PGW  100  connects to an external network (PDN: Packet Data Network etc.). The PCRF  110  determines policies (charging system) regarding QoS control, charging control or the like in the SGW  90  and the PGW  100 . 
     Interfaces between devices in the 3GPP are described hereinafter. An S1-MME interface is defined between the eNB  60  and the MME  80 . An S1-U interface is defined between the eNB  60  and the SGW  90 . An S11 interface is defined between the MME  80  and the SGW  90 . An S5 interface is defined between the SGW  90  and the PGW  100 . A Gx interface is defined between the PGW  100  and the PCRF  110 . Note that the term “interface” may be replaced by the term “reference point”. 
     An interface corresponding to an X2 interface, which is specified as an interface between eNBs, may be defined between the eNB  60  and the 5G base station  70 . Further, an interface corresponding to the S1-U interface may be defined between the 5G base station  70  and the SGW  90 . Note that, in the case where no interface is set between the 5G base station  70  and the SGW  90 , the 5G base station  70  can transmit and receive data to and from the SGW  90  through the eNB  60 . 
     The communication system in  FIG.  2    shows that the UE  50  performs LTE communications with the eNB  60  and performs 5G radio communications with the 5G base station  70  and forms LTE-5G aggregation. It is assumed that a bearer when the UE  50  performs communications through the eNB  60  is different from a bearer when the UE  50  performs communications through the 5G base station  70 . 
     A configuration example of a charging system is described hereinafter with reference to  FIG.  3   . The charging system in  FIG.  3    includes a PGW  100 , a PCRF  110 , an AF (Application Function) entity  120  (which is referred to hereinafter as AF  120 ), an OCS (Online Charging System)  130 , a TDF (Traffic Detection Function) entity  140  (which is referred to hereinafter as TDF  140 ), and an OFCS (Offline Charging System)  150 . In the charging system of  FIG.  3   , the PGW  100  may have a PCEF (Policy and Charging Enforcement Function) and communicate with each device that constitutes the charging system by use of the PCEF. 
     The AF  120  is an application server, and it performs control related to application services to be provided to the UE  50 . The TDF  140  detects a service type, for each flow, of data transmitted or received by the PGW  100  through the PCRF  110 . The OCS  130  and the OFCS  150  perform charging control or the like in accordance with a charging contract of the UE  50 . For example, in the case of a charging contract such as a prepaid service, the OCS  130  having the ability to monitor the traffic at all times performs charging processing. On the other hand, in the case of a monthly charging contract or the like, the OFCS  150  performs charging processing. 
     Interfaces between devices in the 3GPP are described hereinafter. A Gx interface is defined between the PGW  100  and the PCRF  110 . A Gy interface is defined between the PGW  100  and the OCS  130 . A Gz interface is defined between the PGW  100  and the OFCS  150 . Gyn is defined between the TDF  140  and the OCS  130 . Gzn is defined between the TDF  140  and the OFCS  150 . An Sd interface is defined between the TDF  140  and the PCRF  110 . An Sy interface is defined between the PCRF  110  and the OCS  130 . An Rx interface is defined between the PCRF  110  and the AF  120 . 
     The PGW  100  transmits RAT types managed on a bearer-by-bearer basis to each device through the Gx, Gy and Gz interfaces. Further, the PCRF  110  transmits RAT types managed on a bearer-by-bearer basis to each device through the Rx and Sd interfaces. 
     A configuration example of the PGW  100  according to the second embodiment of the present invention is described with reference to  FIG.  4   . The PGW  100  includes a core network communication unit  101 , a management unit  102 , and a PCC (Policy and Charging Control) communication unit  103 . The PCEF is executed by the management unit  102  and the PCC communication unit  103 . 
     The core network communication unit  101  transmits or receives user data related to the UE  50  to and from the SGW  90 . Further, the core network communication unit  101  receives, from the SGW  90 , a RAT type that is used for each bearer assigned to the UE  50 . The core network communication unit  101  outputs information regarding the received RAT type to the management unit  102 . 
     The management unit  102  manages the RAT type in association with the bearer assigned to the UE  50 . An example in which a RAT type is added, in association with a bearer, to a list of parameters managed by the PGW  100  which is specified in 3GPP TS23.401 V13.1.0 (2014-12) Table 5.7.4-1:P-GW context is described with reference to  FIG.  5   . 
     In Field shown in  FIG.  5   , parameters that are managed on a bearer-by-bearer basis by the PGW  100  are written. In Field of  FIG.  5   , EPS (Evolved Packet System) Bearer ID is set. In Field written below EPS Bearer ID of  FIG.  5   , parameters that are managed on a per EPS Bearer ID basis are shown. EPS Bearer is a bearer that is set between the UE  50  and the PGW  100 . 
       FIG.  5    shows that the parameters that are managed on a per EPS Bearer ID basis include a RAT type (which is shown at the bottom). In this manner, the management unit  102  of the PGW  100  manages the RAT type and the EPS Bearer ID in association with each other. 
     Referring back to  FIG.  4   , the PCC communication unit  103  transmits the RAT type that is managed on a per EPS Bearer ID basis in the management unit  102  to the PCRF  110 , the OCS  130  and the OFCS  150 . 
     Note that, also in the case where RAT types are managed on a per UE  50  basis just like the way it used to be, the PCC communication unit  103  transmits the RAT type that is managed on a per EPS Bearer ID basis of  FIG.  5   , in preference to the RAT that is managed on a per UE  50  basis, to the PCRF  110 , the OCS  130  and the OFCS  150 . 
     A configuration example of the eNB  60  according to the second embodiment of the present invention is described with reference to  FIG.  6   . The eNB  60  includes a radio communication unit  61 , a different RAT communication unit  62 , and a core network communication unit  63 . The elements that constitute the eNB  60  may be software, a module or the like whose processing is executed by running, on a processor, a program stored in a memory. Further, the elements that constitute the eNB  60  may be software such as a circuit or a chip. 
     The radio communication unit  61  performs LTE communications with the UE  50 . The different RAT communication unit  62  performs communications with another radio communication device that supports a different radio communication scheme from LTE. In this example, the different RAT communication unit  62  performs communications with the 5G base station  70 . The core network communication unit  63  transmits or receives control data to and from the MME  80 . The control data may be called C(Control)-Plane data, for example. Further, the core network communication unit  63  transmits or receives user data to and from the SGW  90 . The user data may be called U (User)-Plane, for example. Although the core network communication unit  63  transmits or receives control data and user data in this example, a communication unit that transmits or receives control data and a communication unit that transmits or receives user data may be different functional blocks or different interfaces. 
     The different RAT communication unit  62  carries out processing of adding the 5G base station  70  as a device to form the LTE-5G aggregation when the eNB  60  is performing LTE communications with the UE  50 . 
     A configuration example of the UE  50  is described with reference to  FIG.  7   . The UE  50  includes an LTE communication unit  51  and a 5G communication unit  52 . The LTE communication unit  51  performs LTE communications with the eNB  60 . The 5G communication unit  52  performs 5G communications with the 5G base station  70 . The UE  50  communicates with the eNB  60  and the 5G base station  70  at the same time by using the LTE communication unit  51  and the 5G communication unit  52  and thereby form the LTE-5G aggregation. Further, the UE  50  is a terminal capable of performing simultaneous communications (dual connections) using a plurality of different radio access technologies. 
     A process flow of transmitting of a RAT type in the 3GPP according to the second embodiment of the present invention is described hereinafter with reference to  FIG.  8   .  FIG.  8    refers to 3GPP TS23.401 V13.1.0 (2014-12) FIG. 5.4.7-1.  FIG.  8    shows a process flow related to E-UTRAN (Evolved Universal Terrestrial Radio Access Network) initiated E-RAB (EPS-Radio Access Bearer) modification procedure. To be specific,  FIG.  8    shows a process flow of transmitting a RAT type in the case where the 5G base station  70  is added as a device to form the LTE-5G aggregation when the UE  50  and the eNB  60  are performing LTE communications. 
     First, the UE  50 , the eNB  60  and the 5G base station  70  carry out processing to add the 5G base station  70  (SCG (Secondary Cell Group) Modification) (S11). The SCG indicates a base station (or a service cell formed by the base station) that is added to form the LTE-5G aggregation. To be specific, in  FIG.  8   , the 5G base station  70  corresponds to the SCG. On the other hand, the eNB  60 , with which the UE  50  has communicated initially, corresponds to a MCG (Master Cell Group). 
     Next, user data is transferred between the eNB  60  and the 5G base station  70  (Forwarding of data) (S  12 ). 
     Then, the eNB  60  transmits an E-RAB Modification Indication message to the MME  80  in order to update bearer information after addition of the 5G base station  70  as the SCG (S13). The bearer information to be updated is E-RAB (E-UTRAN Radio Access Bearer). The E-RAB is a bearer that is set between the UE  50  and the SGW  90 . Further, the E-RAB corresponds one-to-one with an EPS Bearer that is set between the UE  50  and the PGW  100 . 
     Parameter information that is set to the E-RAB Modification Indication message is described with reference to  FIG.  9   . Note that  FIG.  9    refers to 3GPP TS 36.413 V13.0.0 (2015-06) Section 9.1.3.8. Parameter information that is set to the E-RAB Modification Indication message is written below IE/Group Name. 
     In E-RAB to be Modified List, parameters regarding the 5G base station  70  that is added to form the LTE-5G aggregation are set. For example, in E-RAB to be Modified Item IEs (Information Elements), E-RAB ID for identifying E-RAB to be assigned when the UE  50  communicates with the 5G base station  70  is set. Further, in E-RAB to be Modified Item IEs, RAT type (5G) indicating the RAT which the UE  50  uses for communications with the 5G base station  70  is set. For example, information indicating 5G may be set as the RAT type that is set to E-RAB to be Modified Item IEs. 
     The bearer that is set between the UE  50  and the SGW  90  through the 5G base station  70  may be called differently from E-RAB. In  FIG.  9   , the bearer that is set between the UE  50  and the SGW  90  through the 5G base station  70  is described as E-RAB for the sake of easier explanation. Further, the names E-RAB to be Modified List, E-RAB to be Modified Item IEs, and E-RAB ID may be changed in accordance with the name of the bearer that is set between the UE  50  and the SGW  90  through the 5G base station  70 . 
     In E-RAB not to be Modified List, parameters regarding the eNB  60 , with which the UE  50  has communicated initially, are set. For example, in E-RAB not to be Modified Item IEs, E-RAB ID for identifying E-RAB to be assigned when the UE  50  communicates with the eNB  60  is set. Further, in E-RAB to be Modified Item IEs, RAT type (LTE) indicating the RAT which the UE  50  uses for communications with the eNB  60  is set. For example, information indicating LTE may be set as the RAT type that is set to E-RAB to be Modified Item IEs. 
     The eNB  60  transmits, to the MME  80 , the E-RAB Modification Indication message containing the RAT type associated with the E-RAB ID. 
     Referring back to  FIG.  8   , the MME  80  receives the E-RAB Modification Indication message and transmits, to the SGW  90 , a Modify Bearer Request message to which the RAT type associated with the E-RAB ID is set (S14). Further, the SGW  90  transmits, to the PGW  100 , the Modify Bearer Request message to which the RAT type associated with the E-RAB ID is set (S15). 
     Parameter information that is set to the Modify Bearer Request message is described with reference to  FIG.  10   . Note that  FIG.  10    refers to 3GPP TS 29.274 V13.2.0 (2015-06) Table 7.2.7-2. As shown in  FIG.  10   , a RAT type and EPS Bearer ID are set to the Modify Bearer Request message. Further, when there are a plurality of E-RAB IDs as in the example of  FIG.  9   , a plurality of Bearer Context IE Types are set to the Modify Bearer Request message, and a RAT type is set for each EPS Bearer ID. Further, the RAT type may be set for each Modify Bearer Request message. In other words, the RAT type can be set for each UE in the Modify Bearer Request message. In this case, the RAT type that is set to the Modify Bearer Request message is valid for all EPS Bearers. However, in the case where the RAT type is set to each of the Modify Bearer Request message and the EPS Bearer ID, the RAT type that is set to the EPS Bearer ID may be processed in preference to the other. 
     Referring back to  FIG.  8   , as a response to the Modify Bearer Request message, the PGW  100  transmits a Modify Bearer Response message to the SGW  90  (S16). Further, the SGW  90  transmits the Modify Bearer Response message to the MME  80  (S17). After Step S17, the SGW  90  can transmit user data addressed to the UE  50  to the eNB  60  and the 5G base station  70 . Further, after Step S17, the SGW  90  can receive user data transmitted from the UE  50  through the eNB  60  or the 5G base station  70 . 
     Although the RAT type associated with the E-RAB ID or the EPS Bearer ID is set to the E-RAB Modification Indication message and the Modify Bearer Request message in the process flow of  FIG.  8   , the RAT type associated with a bearer may be set to another message different from those messages. 
     For example,  FIG.  11    shows that a RAT type is set, for each EPS Bearer ID, to a Create Session Request message that is used in an ATTACH process, a Tracking Area Update process or the like. Note that  FIG.  11    refers to 3GPP TS 29.274 V13.2.0 (2015-06) Table 7.2.1-2. The MME  80  transmits, to the SGW  90 , the Create Session Request message that is set as above. Further, the RAT type may be set for each Create Session Request message. In other words, the RAT type can be set for each UE in the Create Session Request message. In this case, the RAT type that is set to the Create Session Request message is valid for all EPS Bearers. However, in the case where the RAT type is set to each of the Create Session Request message and the EPS Bearer ID, the RAT type that is set to the EPS Bearer ID may be processed in preference to the other. Further, the SGW  90  transmits (transfers), to the PGW  100 , the Create Session Request message that is set as above. 
       FIG.  12    shows that a RAT type is set, for each EPS Bearer ID, to a Bearer Resource Command message that is used to request assignment of a bearer when the UE  50  adds the 5G base station  70  and forms the LTE-5G aggregation or to request modification of a bearer. Note that  FIG.  12    refers to 3GPP TS 29.274 V13.2.0 (2015-06) Table 7.2.5-2. The MME  80  transmits, to the SGW  90 , the Bearer Resource Command message that is set as above. Further, the RAT type may be set for each Bearer Resource Command message. In other words, the RAT type can be set for each UE in the Bearer Resource Command message. In this case, the RAT type that is set to the Bearer Resource Command message is valid for all EPS Bearers. However, in the case where the RAT type is set to each of the Bearer Resource Command message and the EPS Bearer ID, the RAT type that is set to the EPS Bearer ID may be processed in preference to the other. Further, the SGW  90  transmits (transfers), to the PGW  100 , the Bearer Resource Command message that is set as above. 
       FIG.  13    shows that a RAT type is set, for each EPS Bearer ID, to an Access Bearers Request message that is used in a handover process where no change occurs in the SGW  90 . Note that  FIG.  13    refers to 3GPP TS 29.274 V13.2.0 (2015-06) Table 7.2.24-2. The MME  80  transmits, to the SGW  90 , the Modify Access Bearers Request message that is set as above. Further, the RAT type may be set for each Modify Access Bearers Request message. In other words, the RAT type can be set for each UE in the Modify Access Bearers Request message. In this case, the RAT type that is set to the Modify Access Bearers Request message is valid for all EPS Bearers. However, in the case where the RAT type is set to each of the Modify Access Bearers Request message and the EPS Bearer ID, the RAT type that is set to the EPS Bearer ID may be processed in preference to the other. 
       FIG.  14    shows that a RAT type is set, for each EPS Bearer ID, to a Context Request message that is used in a Tracking Area Update process or the like. Note that  FIG.  14    refers to 3GPP TS 29.274 V13.2.0 (2015-06) Table 7.3.5-1. The Context Request message is transmitted between an MME before change and an MME after change when the UE  50  moves to a place where a change in the MME occurs. Further, the RAT type may be set for each Context Request message. In other words, the RAT type can be set for each UE in the Context Request message. In this case, the RAT type that is set to the Context Request message is valid for all EPS Bearers. However, in the case where the RAT type is set to each of the Context Request message and the EPS Bearer ID, the RAT type that is set to the EPS Bearer ID may be processed in preference to the other. 
       FIG.  15    shows that a RAT type is set, for each EPS Bearer ID, to a Change Notification Request message that is transmitted from the MME  80  to the SGW  90 . Note that  FIG.  15    refers to 3GPP TS 29.274 V13.2.0 (2015-06) Table 7.3.14-1. Further, the RAT type may be set for each Change Notification Request message. In other words, the RAT type can be set for each UE in the Change Notification Request message. In this case, the RAT type that is set to the Change Notification Request message is valid for all EPS Bearers. However, in the case where the RAT type is set to each of the Change Notification Request message and the EPS Bearer ID, the RAT type that is set to the EPS Bearer ID may be processed in preference to the other. 
     Hereinafter, a process flow when transmitting a RAT type from the PGW  100  to the PCRF  110  is described with reference to  FIG.  16   . 
     When the UE  50  forms the LTE-5G aggregation with the eNB  60  and the 5G base station  70 , the PGW  100  notifies the PCRF  110  that an IP-CAN (IP-Connectivity Access Network) Session is established. To be specific, the PGW  100  transmits a Diameter CCR (Credit Control Request) message to the PCRF  110  (S21). The PGW  100  sets, to the Diameter CCR message, the RAT type associated with the EPS bearer. The PCRF  110  receives the Diameter CCR message and thereby grasps the RAT type associated with the EPS bearer. Further, the RAT type may be set for each Diameter CCR message. In other words, the RAT type can be set for each UE in the Diameter CCR message. In this case, the RAT type that is set to the Diameter CCR message is valid for all EPS Bearers. However, in the case where the RAT type is set to each of the Diameter CCR message and the EPS bearer, the RAT type that is set to the EPS Bearer ID may be processed in preference to the other. 
     A process of transmitting a Diameter message between the PCRF  110  and the TDF  140  is described hereinafter with reference to  FIG.  17   . The PCRF  110  transmits, to the TDF  140 , a Diameter TSR (TDF Session Request) message to which an ADC (Application Detection and Control) rule for extracting a specific packet flow from user data traffic regarding the UE  50  is set (S31). The PCRF  110  sets the RAT type associated with the EPS bearer to the Diameter TSR message. Further, the RAT type may be set for each Diameter TSR message. In other words, the RAT type can be set for each UE in the Diameter TSR message. In this case, the RAT type that is set to the Diameter TSR message is valid for all EPS Bearers. However, in the case where the RAT type is set to each of the Diameter TSR message and the EPS bearer, the RAT type that is set to the EPS Bearer may be processed in preference to the other. 
     After that, the TDF  140  transmits, as a response message, a Diameter TSA (TDF Session Answer) message to the PCRF  110  (S32). 
     Besides the examples shown in  FIGS.  16  and  17   , the RAT type associated with the EPS Bearer is transmitted to the AF  120 , the OCS  130  and the OFCS  150  with use of the Diameter message. Further, the RAT type may be set for each Diameter TSA message. In other words, the RAT type can be set for each UE in the Diameter TSA message. In this case, the RAT type that is set to the Diameter TSA message is valid for all EPS Bearers. However, in the case where the RAT type is set to each of the Diameter TSA message and the EPS bearer, the RAT type that is set to the EPS Bearer may be processed in preference to the other. 
     Values of RAT types to be set to various messages are described hereinbelow. Currently, in 3GPP TS 29.274 V13.2.0 (2015-06) Table 8.17-1, Values 0 to 7 shown in  FIG.  18    are defined as values indicating RAT types. For example, Value 3 indicates wireless LAN (WLAN), and Value 6 indicates EUTRAN (LTE).  FIG.  18    shows that 8 is newly added as the value of the RAT type indicating 5G. It is thereby possible to set 6 when LTE is indicated as the RAT type and set 8 when 5G is indicated in each message. 
     As described above, the RAT type associated with the E-RAB ID or the EPS Bearer ID is set to each message defined in the 3GPP and transmitted to a related node including the PGW  100 . Therefore, when the UE  50  forms the LTE-5G aggregation, the PGW  100  can grasp the RAT type for each bearer used by the UE  50 , not for each UE  50 . The PGW  100  can thereby carry out charging on a bearer-by-bearer basis in accordance with the RAT type for the UE  50  that forms the LTE-5G aggregation. 
     Third Embodiment 
     A configuration example of a communication system according to a third embodiment of the present invention is described with reference to  FIG.  19   . The communication system in  FIG.  19    uses an access point WT  160 , which performs wireless LAN communications, in place of the 5G base station  70  in  FIG.  2   . Further, it is assumed that an interface is not set between the WT  160  and the SGW  90 , and the WT  160  transmits or receives user data regarding the UE  50  through the eNB  60 . An Xw interface is defined between the eNB  60  and the WT  160 . The WT  160  may be an AP (Access Point) or a WiFi router that is used as a master unit or a base station in wireless LAN communications, for example. 
     The communication system in  FIG.  19    shows that the UE  50  performs LTE communications with the eNB  60  and performs wireless LAN communications with the WT  160  and forms the LTE-WT aggregation. It is assumed that the eNB  60  sets a bearer that is used for LTE communications with the UE  50  and a bearer that is used for wireless LAN communications through the WT  160  as one bearer. Specifically, the eNB  60  sets two different RATs to one bearer and thereby forms the LTE-WT aggregation with the UE  50 . 
     Values of RAT types to be set to various messages defined in the 3GPP are described hereinbelow. Currently, in 3GPP TS 29.274 V13.2.0 (2015-06) Table 8.17-1, Values 0 to 7 shown in  FIG.  20    are defined as values indicating RAT types. For example, Value 3 indicates wireless LAN (WLAN), and Value 6 indicates EUTRAN (LTE). 
     In the second embodiment, in the case where the UE  50  forms the LTE-5G aggregation, a predetermined Value may be set for each bearer. However, in the case where the UE  50  forms the LTE-WT aggregation as in the third embodiment, a plurality of RATs are included in one bearer. In such a case, it may be defined that the RAT type of Value 8 indicates EUTRAN+WLAN as shown in  FIG.  20   , for example. Specifically, each node shown in  FIG.  19    may determine that the UE  50  forms the LTE-WT aggregation when Value 8 is set as the RAT type. 
     Alternatively, as shown in  FIG.  21   , it may be indicated that the UE  50  forms the LTE-WT aggregation by writing values next to each other, like Value 6+3. Note that  FIG.  12    refers to 3GPP TS 29.274 V13.2.0 (2015-06) Table 8.17-1. 
     Further, in  FIGS.  20  and  21   , a usage rate, in each RAT, of user data transmitted through one bearer may be also defined when the UE  50  forms the LTE-WT aggregation. 
     For example, in  FIG.  20   , Value 8 may be defined as EUTRAN (30%)+WLAN (70%), and Value 9 may be defined as EUTRAN (50%)+WLAN (50%) or the like. 30% in EUTRAN (30%) means that 30% of user data transmitted through one bearer is transmitted by LTE communications. 
     Further, in  FIG.  21   , a usage rate of LTE communications and WLAN communications may be defined like Value6 (30%)+3 (70%). 
     Parameter information that is set to the E-RAB Modification Indication message according to the third embodiment of the present invention is described with reference to  FIG.  22   . As described earlier, it is assumed in the second embodiment that E-RABs that are identified by different E-RAB IDs are used in the eNB  60  and the 5G base station  70  when the UE  50  forms the LTE-5G aggregation in  FIG.  9   . Thus, in  FIG.  9   , E-RAB to be Modified List and E-RAB not to be Modified List are contained in the E-RAB Modification Indication message. 
     On the other hand, in  FIG.  22   , it is assumed that the same E-RAB is used in the eNB  60  and the WT  160  when the UE  50  forms the LTE-WT aggregation. Thus, in  FIG.  9   , only E-RAB to be Modified List is contained in the E-RAB Modification Indication message. In E-RAB to be Modified List, a RAT type is set in association with the E-RAB ID. When the UE  50  forms the LTE-WT aggregation, Value where the RAT types indicate EUTRAN+WLAN in  FIG.  20  or  21    is set as the RAT type in  FIG.  22   . 
     Further, the name of a bearer where LTE communications and wireless LAN communications are set may be different from E-RAB, and it is not limited to the name E-RAB. 
     As described above, by defining RAT types as in the third embodiment of the present invention, the PGW  100  can accurately grasp the RAT types that are set to one bearer even when a plurality of RAT types are set to one bearer. 
     Further, by setting a usage rate of each RAT type in the case where a plurality of RAT types are set to one bearer, the PGW  100  can carry out charging for the UE  50  in accordance with the usage rate of the RAT type in charging control. 
     It should be noted that the present invention is not limited to the above-described embodiments and may be varied in many ways within the scope of the present invention. For example, the LTE-5G aggregation in the second embodiment may be implemented by using one bearer as described in the third embodiment. Further, the LTE-WT aggregation in the third embodiment may be implemented by using two bearers as described in the second embodiment. 
     Configuration examples of the UE  50 , and the eNB  60  and the PGW  100  described in the plurality of embodiments above are described hereinafter.  FIG.  23    is a block diagram showing a configuration example of the eNB  60 . Referring to  FIG.  23   , the eNB  60  includes an RF transceiver  1001 , a network interface  1003 , a processor  1004 , and a memory  1005 . The RF transceiver  1001  performs analog RF signal processing for communication with the UEs. The RF transceiver  1001  may include a plurality of transceivers. The RF transceiver  1001  is connected to an antenna  1002  and a processor  1004 . The RF transceiver  1001  receives modulated symbol data (or OFDM symbol data) from the processor  1004 , generates a transmission RF signal and supplies the transmission RF signal to the antenna  1002 . Further, the RF transceiver  1001  generates a baseband received signal based on a received RF signal received by the antenna  1002  and supplies it to the processor  1004 . 
     The network interface  1003  is used for communications with a network node (e.g., other eNBs, Mobility Management Entity (MME), Serving Gateway (S-GW), and TSS or ITS server). The network interface  1003  may include a network interface card (NIC) compliant to IEEE 802.3 series, for example. 
     The processor  1004  performs data plane processing including digital baseband signal processing and control plane processing for radio communications. For example, in the case of LTE and LTE-Advanced, the digital baseband signal processing by the processor  1004  may include signal processing of PDCP layer, RLC layer, MAC layer and PHY layer. Further, the signal processing by the processor  1004  may include signal processing of GTP-U·UDP/IP layer in the X2-U interface and the S1-U interface. Furthermore, the control plane processing by the processor  1004  may include processing of X2AP protocol, S1-MME protocol and RRC protocol. 
     The processor  1004  may include a plurality of processors. For example, the processor  1004  may include a modem processor (e.g., DSP) that performs digital baseband signal processing, a processor (e.g., DSP) that performs signal processing of GTP-U·UDP/IP layer in the X2-U interface and the S1-U interface, and a protocol stack processor (e.g., CPU or MPU) that performs control plane processing. 
     The memory  1005  is a combination of a volatile memory and a nonvolatile memory. The memory  1005  may include a plurality of memory devices that are physically independent of one another. The volatile memory is a Static Random Access Memory (SRAM), a Dynamic RAM (DRAM), or a combination of them, for example. The nonvolatile memory is a mask Read Only Memory (MROM), an Electrically Erasable Programmable ROM (EEPROM), a flash memory, a hard disk drive, or a combination of them, for example. The memory  1005  may include a storage that is placed apart from the processor  1004 . In this case, the processor  1004  may access the memory  1005  through the network interface  1003  or an I/O interface, which is not shown. 
     The memory  1005  may store a software module (computer program) containing a group of instructions and data for performing the processing by the eNB  40  described in the above plurality of embodiments. In several implementations, the processor  1004  may be configured to perform the processing of the eNB  60  described in the above embodiments by reading the software module from the memory  1005  and executing it. 
       FIG.  24    is a block diagram showing a configuration example of the UE  50 . A Radio Frequency (RF) transceiver  1101  performs analog RF signal processing for communication with the eNB  60  and the 5G base station  70 . The analog RF signal processing performed by the RF transceiver  1101  includes frequency up-conversion, frequency down-conversion, and amplification. The RF transceiver  1101  is connected to an antenna  1102  and a baseband processor  1103 . Specifically, the RF transceiver  1101  receives modulated symbol data (or OFDM symbol data) from the baseband processor  1103 , generates a transmission RF signal and supplies the transmission RF signal to the antenna  1102 . Further, the RF transceiver  1101  generates a baseband received signal based on a received RF signal received by the antenna  1102  and supplies it to the baseband processor  1103 . 
     The baseband processor  1103  performs digital baseband signal processing (data plane processing) and control plane processing for radio communications. The digital baseband signal processing includes (a) data compression/decompression, (b) data segmentation/concatenation, (c) transmission format (transmission frame) composition/decomposition, (d) transmission path encoding/decoding, (e) modulation (symbol mapping)/demodulation, and (f) OFDM symbol data (baseband OFDM signal) generation by Inverse Fast Fourier Transform (IFFT) and the like. On the other hand, the control plane processing includes communication management of Layer  1  (e.g., transmission power control), Layer  2  (e.g., radio resource management and hybrid automatic repeat request (HARQ) processing), and Layer  3  (e.g., attach, mobility, and signaling related to call management). 
     For example, in the case of LTE and LTE-Advanced, the digital baseband signal processing by the baseband processor  1103  may include signal processing of Packet Data Convergence Protocol (PDCP) layer, Radio Link Control (RLC) layer, MAC layer, and PHY layer. Further, the control plane processing by the baseband processor  1103  may include processing of Non-Access Stratum (NAS) protocol, RRC protocol, and MAC CE. 
     The baseband processor  1103  may include a modem processor (e.g., Digital Signal Processor (DSP)) that performs digital baseband signal processing and a protocol stack processor (e.g., Central Processing Unit (CPU) or Micro Processing Unit (MPU)) that performs control plane processing. In this case, the protocol stack processor that performs control plane processing may be made common to an application processor  1104 , which is described below. 
     The application processor  1104  is also called a CPU, an MPU, a microprocessor or a processor core. The application processor  1104  may include a plurality of processors (a plurality of processor cores). The application processor  1104  implements each function of the UE  50  by running a system software program (Operating System (OS)) and various application programs (e.g., call application, web browser, mailer, camera control application, music playback application etc.) read from a memory  1106  or a memory, which is not shown. 
     In several implementations, as shown in the dotted line ( 1105 ) in  FIG.  24   , the baseband processor  1103  and the application processor  1104  may be integrated into one chip. In other words, the baseband processor  1103  and the application processor  1104  may be implemented as one System on Chip (SoC) device  1105 . The SoC device is also called a system Large Scale Integration (LSI) or a chip set in some cases. 
     The memory  1106  is a volatile memory, a nonvolatile memory, or a combination of them. The memory  1106  may include a plurality of memory devices that are physically independent of one another. The volatile memory is a Static Random Access Memory (SRAM), a Dynamic RAM (DRAM), or a combination of them, for example. The nonvolatile memory is a mask Read Only Memory (MROM), an Electrically Erasable Programmable ROM (EEPROM), a flash memory, a hard disk drive, or a combination of them, for example. For example, the memory  1106  may include an external memory device that is accessible from the baseband processor  1103 , the application processor  1104  and the SoC  1105 . The memory  1106  may include an internal memory device that is integrated into the baseband processor  1103 , the application processor  1104  or the SoC  1105 . Further, the memory  1106  may include a memory in a Universal Integrated Circuit Card (UICC). 
     The memory  1106  may store a software module (computer program) containing a group of instructions and data for performing the processing by the UE  50  described in the above plurality of embodiments. In several implementations, the baseband processor  1103  or the application processor  1104  may be configured to perform the processing of the UE  50  described in the above embodiments by reading the software module from the memory  1106  and executing it. 
       FIG.  25    is a block diagram showing a configuration example of the PGW  100 . Referring to  FIG.  25   , the PGW  100  includes a network interface  1211 , a processor  1202 , and a memory  1203 . The network interface  1201  is used to communicate with network nodes (e.g., the eNodeB  130 , MME, P-GW). The network interface  1201  may include a network interface card (NIC) that complies with the IEEE 802.3 series, for example. 
     The processor  1202  reads and runs software (computer program) from the memory  1203  and thereby executes processing of the PGW  100  that is described with reference to the sequence charts and the flowcharts in the embodiments described above. The processor  1202  may be a microprocessor, an MPU or a CPU, for example. The processor  1202  may include a plurality of processors. 
     The memory  1203  is a combination of a volatile memory and a nonvolatile memory. The memory  1203  may include a storage that is placed apart from the processor  1202 . In this case, the processor  1202  may access the memory  1203  through an I/O interface, which is not shown. 
     In the example of  FIG.  25   , the memory  1203  is used to store a group of software modules. The processor  1202  reads and runs the group of software modules from the memory  1203  and can thereby perform the processing of the PGW  100  described in the above embodiments. 
     As described with reference to  FIGS.  23  and  25   , each of processors included in the UE  50 , the eNB  60  and the PGW  100  runs one or a plurality of programs including a group of instructions for causing a computer to perform the algorithms described using the drawings. 
     In the above example, the program can be stored and provided to the computer using any type of non-transitory computer readable medium. The non-transitory computer readable medium includes any type of tangible storage medium. Examples of the non-transitory computer readable medium include magnetic storage media (such as floppy disks, magnetic tapes, hard disk drives, etc.), optical magnetic storage media (e.g. magneto-optical disks), CD-ROM (Read Only Memory), CD-R, CD-R/W, DVD-ROM (Digital Versatile Disc Read Only Memory), DVD-R (DVD Recordable)), DVD-R DL (DVD-R Dual Layer)), DVD-RW (DVD ReWritable)), DVD-RAM), DVD+R), DVR+R DL), DVD+RW), BD-R (Blu-ray (registered trademark) Disc Recordable)), BD-RE (Blu-ray (registered trademark) Disc Rewritable)), BD-ROM), and semiconductor memories (such as mask ROM, PROM (Programmable ROM), EPROM (Erasable PROM), flash ROM, RAM (Random Access Memory), etc.). The program may be provided to a computer using any type of transitory computer readable medium. Examples of the transitory computer readable medium include electric signals, optical signals, and electromagnetic waves. The transitory computer readable medium can provide the program to a computer via a wired communication line such as an electric wire or optical fiber or a wireless communication line. 
     While the invention has been particularly shown and described with reference to embodiments thereof, the invention is not limited to these embodiments. It will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the claims. 
     This application is based upon and claims the benefit of priority from Japanese patent application No. 2015-180484 filed on Sep. 14, 2015, the disclosure of which is incorporated herein in its entirety by reference. 
     Further, the whole or part of the embodiments disclosed above can be described as, but not limited to, the following supplementary notes. 
     Supplementary Note 1 
     A gateway device comprising: 
     a management unit configured to, when a communication terminal forms communication aggregation by performing a first radio communication using a first radio access technology and a second radio communication using a second radio access technology, manage at least one bearer assigned to the communication terminal in association with information indicating the first and second radio access technologies; and 
     a charging system communication unit configured to transmit the information indicating the first and second radio access technologies to at least one charging control device that performs charging control. 
     Supplementary Note 2 
     The gateway device according to Supplementary Note 1, wherein the charging system communication unit transmits, to the at least one charging control device, a Diameter message to which the information indicating the radio access technology is set. 
     Supplementary Note 3 
     The gateway device according to Supplementary Note 1 or 2, wherein, when a first bearer is assigned to the first radio communication and a second bearer is assigned to the second radio communication, the management unit manages the first bearer in association with first type information indicating the first radio access technology, and manages the second bearer in association with second type information indicating the second radio access technology. 
     Supplementary Note 4 
     The gateway device according to Supplementary Note 3, wherein 
     the management unit further manages the first bearer and the first type information in association with the second bearer and the second type information, and manages the communication terminal in association with the first type information, and 
     the charging system communication unit transmits, to the charging control device, the first type information associated with the first bearer and the second type information associated with the second bearer in preference to the first type information associated with the communication terminal. 
     Supplementary Note 5 
     The gateway device according to Supplementary Note 1 or 2, wherein, when a third bearer is assigned to the first and second radio communications, the management unit manages the third bearer in association with third type information indicating the first radio access technology and the second radio access technology. 
     Supplementary Note 6 
     The gateway device according to Supplementary Note 5, wherein 
     the management unit further manages the third bearer in association with the third type information, and manages the communication terminal in association with the first type information indicating the first radio access technology, and 
     the charging system communication unit transmits, to the charging control device, the third type information associated with the third bearer in preference to the first type information associated with the communication terminal. 
     Supplementary Note 7 
     The gateway device according to any one of Supplementary Notes 1 to 6, further comprising: 
     a core network communication unit configured to receive a control message associating at least one bearer assigned to the communication terminal with information regarding the first and second radio access technologies from a network device that performs control related to transmission of user data between the gateway device and a first radio communication device that performs the first radio communication and a second radio communication device that performs the second radio communication. 
     Supplementary Note 8 
     The gateway device according to Supplementary Note 7, wherein the control message includes at least one of a Create Session Request message, a Bearer Resource Command message, a Modify Bearer Request message, a Modify Access Bearers Request message, a Context Request message, and a Change Notification Request message. 
     Supplementary Note 9 
     A radio communication device that performs a first radio communication using a first radio access technology with a communication terminal, wherein, when the communication terminal forms communication aggregation by performing the first radio communication and a second radio communication using a second radio access technology, the radio communication device transmits information associating at least one bearer assigned to the communication terminal and information indicating the first and second radio access technologies to a network device that manages the bearer. 
     Supplementary Note 10 
     A charging control method comprising: 
     when a communication terminal forms communication aggregation by performing a first radio communication using a first radio access technology and a second radio communication using a second radio access technology, managing at least one bearer assigned to the communication terminal in association with information indicating the first and second radio access technologies; and 
     transmitting the information indicating the first and second radio access technologies to at least one charging control device that performs charging control. 
     Supplementary Note 11 
     A data transmission method used in a radio communication device that performs a first radio communication using a first radio access technology with a communication terminal, comprising: 
     when the communication terminal forms communication aggregation by performing the first radio communication and a second radio communication using a second radio access technology, transmitting information associating at least one bearer assigned to the communication terminal and information indicating the first and second radio access technologies to a network device that manages the bearer. 
     Supplementary Note 12 
     A program causing a computer to execute: 
     when a communication terminal forms communication aggregation by performing a first radio communication using a first radio access technology and a second radio communication using a second radio access technology, managing at least one bearer assigned to the communication terminal in association with information indicating the first and second radio access technologies; and 
     transmitting the information indicating the first and second radio access technologies to at least one charging control device that performs charging control. 
     Supplementary Note 13 
     A program to be executed by a computer that performs a first radio communication using a first radio access technology with a communication terminal, the program causing the computer to execute: 
     when the communication terminal forms communication aggregation by performing the first radio communication and a second radio communication using a second radio access technology, transmitting information associating at least one bearer assigned to the communication terminal and information indicating the first and second radio access technologies to a network device that manages the bearer. 
     REFERENCE SIGNS LIST 
     
         
           10  COMMUNICATION TERMINAL 
           21  RADIO COMMUNICATION DEVICE 
           22  RADIO COMMUNICATION DEVICE 
           30  GATEWAY DEVICE 
           31  MANAGEMENT UNIT 
           32  CHARGING SYSTEM COMMUNICATION UNIT 
           40  CHARGING CONTROL DEVICE 
           50  UE 
           51  LTE COMMUNICATION UNIT 
           52  5G COMMUNICATION UNIT 
           60  eNB 
           61  RADIO COMMUNICATION UNIT 
           62  DIFFERENT RAT COMMUNICATION UNIT 
           63  CORE NETWORK COMMUNICATION UNIT 
           70  5G BASE STATION 
           80  MME 
           90  SGW 
           100  PGW 
           101  CORE NETWORK COMMUNICATION UNIT 
           102  MANAGEMENT UNIT 
           103  PCC COMMUNICATION UNIT 
           110  PCRF 
           120  AF 
           130  OCS 
           140  TDF 
           150  OFCS 
           160  WT