Patent Publication Number: US-2013252580-A1

Title: Communication system, service control device, and communication method

Description:
TECHNICAL FIELD 
     The present invention relates to a communication system for a mobile terminal, a service control device used in the communication system, and a communication method executed on the communication system. 
     BACKGROUND ART 
     Conventionally, there has been a communication system for a mobile terminal using a General Packet Radio Service (GPRS). This communication system includes a communication control device that calculates a communication fee for the mobile terminal. The communication control device is a Gateway GPRS Support Node (GGSN) that is a gateway switch for connection between different networks, a Service GPRS Support Node (SGSN) that is a switch arranged subordinate to the GGSN, or the like. 
     For the mobile terminal utilizing the communication system described above, usage fee is charged. For example, a prepaid charging scheme in which a usage fee for communication is paid in advance so that communication of a mobile terminal within a range of a communication volume corresponding to the paid fee is possible is disclosed in Patent Literature 1. 
     CITATION LIST 
     Patent Literature 
     [Patent Literature 1] Japanese Patent Application Laid-Open Publication No. 2005-204323 
     SUMMARY OF INVENTION 
     Technical Problem 
     In a prepaid charging scheme, it is generally conceivable to store a charge remaining amount corresponding to the communication volume in which communication is possible in a service control device under the management of a communication carrier. In this case, a user of the mobile terminal for example can access the service control device to know the charge remaining amount. 
     However, since the communication volume of the mobile terminal in communication is calculated not in the service control device but in a communication control device, there has been a possibility that a real-time notification of the charge remaining amount in accordance with the current communication is not feasible when the remaining amount of charge is inquired during communication. 
     Thus, it is an object of the present invention to provide a communication system, a service control device, and a communication method with which a real-time notification of a charge remaining amount of a mobile terminal in communication is feasible. 
     Solution to Problem 
     A communication system according to the present invention is a communication system including a communication control device that calculates a communication volume of a mobile terminal and a service control device that stores a charge remaining amount corresponding to a communication volume available to the mobile terminal, wherein the service control device includes communication state storage means for storing information indicating a communication state of the mobile terminal, inquiry acceptance means for accepting an inquiry for the charge remaining amount of the mobile terminal, communication state determination means for determining whether the mobile terminal is in communication on the basis of the information stored in the communication state storage means, updated remaining amount acquisition means for acquiring the charge remaining amount updated in accordance with the communication volume calculated by the communication control device when the communication state determination means determines that the mobile terminal is in communication, and remaining amount notification means for notifying of the charge remaining amount of the mobile terminal in response to the inquiry that the inquiry acceptance means has accepted. 
     In addition, a service control device according to the present invention is a service control device that, in a communication system including a communication control device calculating a communication volume of a mobile terminal, stores a charge remaining amount corresponding to a communication volume available to the mobile terminal, including communication state storage means for storing information indicating a communication state of the mobile terminal, inquiry acceptance means for accepting an inquiry for the charge remaining amount of the mobile terminal, communication state determination means for determining whether the mobile terminal is in communication on the basis of the information stored in the communication state storage means, updated remaining amount acquisition means for acquiring the charge remaining amount updated in accordance with the communication volume calculated by the communication control device when the communication state determination means determines that the mobile terminal is in communication, and remaining amount notification means for notifying of the charge remaining amount of the mobile terminal in response to the inquiry that the inquiry acceptance means has accepted. 
     In addition, a communication method according to the present invention is a communication method executed by a communication system including a communication control device that calculates a communication volume of a mobile terminal and a service control device that stores a charge remaining amount corresponding to a communication volume available to the mobile terminal, including a communication state storage step of, by the service control device, storing information indicating a communication state of the mobile terminal, an inquiry acceptance step of, by the service control device, accepting an inquiry for the charge remaining amount of the mobile terminal, a communication state determination step of, by the service control device, determining whether the mobile terminal is in communication on the basis of the information stored in the communication state storage step, an updated remaining amount acquisition step of, by the service control device, acquiring the charge remaining amount updated in accordance with the communication volume calculated by the communication control device when it is determined that the mobile terminal is in communication in the communication state determination step, and a remaining amount notification step of, by the service control device, notifying of the charge remaining amount of the mobile terminal in response to the inquiry accepted in the inquiry acceptance step. 
     With such a communication system, service control device, and communication method, when the charge remaining amount of the mobile terminal is inquired, whether that mobile terminal is in communication is determined by the service control device. In the case where that mobile terminal is in communication, the charge remaining amount updated in accordance with the communication volume calculated by the communication control device is acquired and notified. Therefore, a real-time notification of the charge remaining amount of the mobile terminal in communication is feasible. In addition, the charge remaining amount of the mobile terminal in communication is acquired after the service control device received the inquiry for the charge remaining amount. Therefore, it is not necessary to continue updating the charge remaining amount stored in the service control device in preparation for an inquiry during communication, and the load on the communication control device and the service control device is reduced. 
     Herein, in a specific example of the communication system, the communication control device may be a switch arranged for each communication area. In this case, the load in a process of calculating the communication volume of the mobile terminal is distributed to the switch arranged for each communication area. 
     In addition, in another specific example of the communication system, the communication control device may be a gateway switch for connection to an external network and include communication state transmission means for transmitting the information indicating the communication state of the mobile terminal, and the communication state storage means in the service control device stores the information indicating the communication state of the mobile terminal transmitted by the communication state transmission means. In this case, the information indicating the communication state of the mobile terminal is transmitted from the gateway switch involved with the communication state of the mobile terminal and therefore is acquired and stored in the service control device reliably. 
     In yet another specific example of the communication system, in the communication control device, the communication state transmission means transmits an address of the gateway switch, and in the service control device, the communication state storage means stores the address of the gateway switch transmitted by the communication state transmission means, and the communication state determination means determines whether the mobile terminal is in communication on the basis of whether the address of the gateway switch is stored in the communication state storage means. In this case, the address for identifying the gateway switch is also utilized in the determination on whether the mobile terminal is in communication, and the data volume that the communication state storage unit should store is reduced. 
     Advantageous Effects of Invention 
     With the communication system, the service control device, and the communication method according to the present invention, a real-time notification of the charge remaining amount of the mobile terminal in communication is feasible. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view illustrating an overall configuration of one embodiment of a communication system according to the present invention. 
         FIG. 2  is a function block diagram of a GGSN that calculates a communication volume. 
         FIG. 3  is a function block diagram of a service control device. 
         FIG. 4  is a flowchart illustrating the procedure of a charge remaining amount notification process. 
         FIG. 5  is a function block diagram of an SGSN that calculates the communication volume. 
         FIG. 6  is a flowchart illustrating the procedure of a charge remaining amount notification process in the case where the SGSN calculates the communication volume. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A preferred embodiment of a service control device and a communication system applied with a communication method according to the present invention will be described below with reference to the drawings. Note that, in the description of the drawings, the same component is denoted by the same reference numeral, and redundant descriptions are omitted. 
       FIG. 1  is a view illustrating an overall configuration of one embodiment of a communication system according to the present invention, and a communication system  1  is a communication system using a GPRS. As illustrated in  FIG. 1 , the communication system  1  includes an SGSN  10  that is a switch, a GGSN  20  that is a gateway switch, and a service control device  30 . The service control device  30  is a home location register (HLR), for example. The communication system  1  is utilized in the communication of a mobile terminal  40  for which a prepaid charging scheme is selected, but is also applicable in a postpaid charging scheme. The mobile terminal  40  connects to a network  50  via the SGSN  10  and the GGSN  20  and performs packet communication with a connection destination  60  on the network  50 . 
     A user of the mobile terminal  40  can pay a usage fee in advance to a communication carrier managing the communication system  1  and perform packet communication up to a communication packet volume corresponding to the paid fee. A charge remaining amount corresponding to the available communication packet volume is stored in the service control device  30 . The communication packet volume of the mobile terminal  40  in communication is calculated by the GGSN  20 , and the charge remaining amount decreases in accordance with a calculation result. That is, the GGSN  20  is a communication control device that calculates the communication packet volume of the mobile terminal  40 . The service control device  30  includes a charge site  70  that is publicly open on a network. The charge site  70  is an interface accessible to the user, for example, of the mobile terminal  40 . For example, the user of the mobile terminal  40  can access the charge site  70  with a personal computer  80  to know the charge remaining amount of the mobile terminal  40 . The charge site  70  can also be accessed from the mobile terminal  40  that is the terminal itself. 
       FIG. 2  is a function block diagram of the GGSN that calculates the communication volume. As illustrated in  FIG. 2 , the GGSN  20  includes a communication control unit  21 , a communication state transmission unit  22 , a communication volume calculation unit  23 , a stored remaining amount reception unit  24 , a remaining amount update unit  25 , and an updated remaining amount transmission unit  26 . 
     The communication control unit  21  performs communication control as a gateway switch. The communication state transmission unit  22  transmits an address of the GGSN  20  to the service control device  30 . 
     The GGSN  23  calculates the communication packet volume of the mobile terminal  40 . The stored remaining amount reception unit  24  acquires the charge remaining amount stored in the service control device  30  upon start of communication of the mobile terminal  40 . The remaining amount update unit  25  subtracts the communication packet volume calculated by the communication volume calculation unit  23  from the charge remaining amount acquired by the stored remaining amount reception unit  24  and updates the charge remaining amount. The updated remaining amount transmission unit  26  transmits the charge remaining amount updated in the remaining amount update unit  25  to the service control device  30 . 
       FIG. 3  is a function block diagram of the service control device. As illustrated in  FIG. 3 , the service control device  30  includes a remaining amount storage unit  31 , a stored remaining amount transmission unit  32 , an updated remaining amount reception unit  33 , a communication state reception unit  34 , a communication state storage unit  35 , a communication state determination unit  36 , an inquiry acceptance unit  37 , and a remaining amount notification unit  38 . 
     The remaining amount storage unit  31  stores the charge remaining amount of the mobile terminal  40 . The stored remaining amount transmission unit  32  transmits the charge remaining amount stored in the remaining amount storage unit  31  to the stored remaining amount reception unit  24  of the GGSN  20 . The updated remaining amount reception unit  33  receives the charge remaining amount updated in the remaining amount update unit  25  of the GGSN  20  from the updated remaining amount transmission unit  26 . When communication of the mobile terminal  40  is terminated, the charge remaining amount updated by the remaining amount update unit  25  of the GGSN  20  is received by the updated remaining amount reception unit  33  from the updated remaining amount transmission unit  26  and stored in the remaining amount storage unit  31 . 
     The communication state reception unit  34  receives the address of the GGSN  20  transmitted from the communication state transmission unit  22  of the GGSN  20 . The communication state storage unit  35  stores the address of the GGSN  20  that the communication state reception unit  34  has received. The communication state storage unit  35  discards the stored address of the GGSN  20  when communication of the mobile terminal  40  is terminated. The discarding of the address of the GGSN  20  by the communication state storage unit  35  is performed on the basis of a termination notification signal sent from the GGSN  20 , for example. The communication state determination unit  36  determines that the mobile terminal  40  is in communication in the case where the address of the GGSN  20  is stored in the communication state storage unit  35  but determines that the mobile terminal  40  is not in communication in the case where it is not stored. That is, in this embodiment, the address of the GGSN  20  is information indicating the communication state of the mobile terminal  40 . The address of the GGSN  20  stored in the communication state storage unit  35  is used to identify the GGSN  20  in the transmission of the charge remaining amount to the GGSN  20  from the stored remaining amount transmission unit  32  and the reception of the charge remaining amount by the updated remaining amount reception unit  33  from the GGSN  20 . 
     The inquiry acceptance unit  37  accepts an inquiry for the charge remaining amount of the mobile terminal  40  via the charge site  70  described above. The remaining amount notification unit  38  notifies of the charge remaining amount of the mobile terminal  40  in response to the inquiry that the inquiry acceptance unit  37  has accepted. The remaining amount notification unit  38  refers to a determination result of the communication state determination unit  36 , and acquires the charge remaining amount with the updated remaining amount reception unit  33  and outputs the acquired charge remaining amount to the charge site  70  in the case where the mobile terminal  40  is in communication. The remaining amount notification unit  38  outputs the charge remaining amount stored in the remaining amount storage unit  31  to the charge site  70  in the case where the mobile terminal  40  is not in communication. 
     The operation of the communication system  1  described above will be described with reference to  FIG. 4 .  FIG. 4  is a flowchart illustrating the procedure of a charge remaining amount notification process. First, the mobile terminal  40  requests a location registration from an SGSN  10  upon entering a service area of the SGSN  10  (step S 101 ). The SGSN  10  that has performed the location registration of the mobile terminal  40  transmits the address of the SGSN  10  to the service control device  30  (step S 102 ). 
     The mobile terminal  40  sends a communication request with the connection destination  60  described above with respect to the SGSN  10  that the mobile terminal  40  is within the range of (step S 103 ). The SGSN  10  that has received the communication request requests connection to the network  50  described above from a GGSN  20  (step S 104 ). The GGSN  20  that has received a connection request connects to the network  50  described above and performs a process that enables communication of the mobile terminal  40  and the connection destination  60  (step S 105 ). 
     Next, the GGSN  20  transmits information (the address of the GGSN  20 ) indicating the communication state of the mobile terminal  40  from the communication state transmission unit  22  to the service control device  30  (step S 106 ). The service control device  30  receives the address of the GGSN  20  with the communication state reception unit  34  and stores it in the communication state storage unit  35  (step S 107 ). 
     Next, the service control device  30  transmits the charge remaining amount stored in the remaining amount storage unit  31  from the stored remaining amount transmission unit  32  to the GGSN  20  (step S 108 ). A transmission destination in step S 108  is identified by the address of the GGSN  20  stored in the communication state storage unit  35 . The GGSN  20  receives the charge remaining amount with the stored remaining amount reception unit  24  and performs an update of the charge remaining amount with the remaining amount update unit  25  (step S 109 ). 
     When the user of the mobile terminal  40 , for example, inputs the inquiry for the charge remaining amount to the charge site  70 , the service control device  30  accepts the inquiry for the charge remaining amount with the inquiry acceptance unit  37  (step S 110 ). Next, the service control device  30  determines with the communication state determination unit  36  whether the mobile terminal  40  is in communication (step S 111 ). 
     When the communication state determination unit  36  determines that the mobile terminal  40  is in communication, the service control device  30  requests the updated charge remaining amount from the GGSN  20  (step S 112 ). A request destination in step S 112  is identified by the address of the GGSN  20  stored in the communication state storage unit  35 . The GGSN  20  that has received a request for the charge remaining amount transmits the charge remaining amount from the updated remaining amount transmission unit  26  to the service control device  30  (step S 113 ). The service control device  30  receives the charge remaining amount with the updated remaining amount reception unit  33  and outputs the received charge remaining amount from the remaining amount notification unit  38  to the charge site  70  (step S 114 ). Accordingly, the charge remaining amount is notified to, for example, the user of the mobile terminal  40 . 
     When the communication state determination unit  36  determines that the mobile terminal  40  is not in communication, the service control device  30  outputs the charge remaining amount stored in the remaining amount storage unit  31  from the remaining amount notification unit  38  to the charge site  70  (step S 114 ). 
     With the communication system  1  described above, the communication packet volume is calculated by the communication volume calculation unit  23  of the GGSN  20  and the charge remaining amount is updated by the remaining amount update unit  25  while the mobile terminal  40  is in a call. When the charge remaining amount of the mobile terminal  40  is inquired, whether the mobile terminal  40  is in communication is determined by the communication state determination unit  36  of the service control device  30 . In the case where the mobile terminal  40  is in communication, the charge remaining amount updated by the remaining amount update unit  25  of the GGSN  20  is acquired and notified by the updated remaining amount reception unit  33 . Therefore, a real-time notification of the charge remaining amount of the mobile terminal  40  in communication is feasible. In addition, the charge remaining amount of the mobile terminal  40  in communication is acquired after the service control device  30  received the inquiry for the charge remaining amount. Therefore, it is not necessary to continue updating the charge remaining amount stored in the service control device  30  in preparation for an inquiry during communication, and the load on the GGSN  20  and the service control device  30  is reduced. 
     In addition, in the communication system  1 , the communication control device that calculates the communication packet volume of the mobile terminal  40  is the GGSN  20 . The communication state transmission unit  22  of the GGSN  20  transmits the address of the GGSN  20  as the information indicating the communication state of the mobile terminal  40 . The communication state storage unit  35  of the service control device  30  stores the address of the GGSN  20  transmitted by the communication state transmission unit  22 . The information indicating the communication state of the mobile terminal  40  is transmitted from the GGSN  20  involved with the communication state of the mobile terminal  40  in this manner and therefore is acquired and stored in the service control device  30  reliably. 
     In addition, the stored remaining amount transmission unit  32  of the service control device  30  identifies the GGSN  20  at the transmission destination of the charge remaining amount on the basis of the address of the GGSN  20  stored in the communication state storage unit  35 . The updated remaining amount reception unit  33  identifies the GGSN  20  at the request destination of the charge remaining amount on the basis of the address of the GGSN  20  stored in the communication state storage unit  35 . Since the GGSN  20  is identified on the basis of the address stored in advance in the communication state storage unit  35  in this manner, a prompt notification of the charge remaining amount in accordance with the current communication becomes possible. 
     Furthermore, the communication state determination unit  36  determines whether the mobile terminal  40  is in communication on the basis of whether the address of the GGSN  20  is stored in the communication state storage unit  35 . In this manner, the address for identifying the GGSN  20  is also utilized in the determination on whether the mobile terminal  40  is in communication, and the data volume that the communication state storage unit  35  should store is reduced. Since the address of the GGSN  20  is discarded when the communication of the mobile terminal  40  is terminated, the data volume that the communication state storage unit  35  should store is reduced further. 
     Note that the communication control device that calculates the communication packet volume of the mobile terminal  40  may be the SGSN  10  instead of the GGSN  20 . The configuration and the operation in this case will be described below. 
       FIG. 5  is a function block diagram of the SGSN that calculates the communication volume. As illustrated in  FIG. 5 , the SGSN  10  includes a communication control unit  11 , a communication state transmission unit  12 , a communication volume calculation unit  13 , a stored remaining amount reception unit  14 , a remaining amount update unit  15 , and an updated remaining amount transmission unit  16 . 
     The communication control unit  11  performs communication control as a switch. The communication state transmission unit  12  transmits the address of the SGSN  10  to the service control device  30 . 
     The communication volume calculation unit  13  calculates the communication packet volume of the mobile terminal  40 . The stored remaining amount reception unit  14  acquires the charge remaining amount stored in the service control device  30  upon start of communication of the mobile terminal  40 . The remaining amount update unit  15  subtracts the communication packet volume calculated by the communication volume calculation unit  13  from the charge remaining amount acquired by the stored remaining amount reception unit  14  and updates the charge remaining amount. The updated remaining amount transmission unit  16  transmits the charge remaining amount updated by the remaining amount update unit  15  to the service control device  30 . 
     In the case where the SGSN  10  calculates the communication packet volume, the communication state reception unit  34  of the service control device  30  receives the address of the SGSN  10  transmitted from the communication state transmission unit  12  in the SGSN  10 . In addition, the communication state reception unit  34  receives the address of the GGSN  20  transmitted from the GGSN  20 . 
     The communication state storage unit  35  stores the addresses of the SGSN  10  and the GGSN  20  that the communication state reception unit  34  has received and discards the address of the GGSN  20  upon the communication of the mobile terminal  40  being terminated. The communication state storage unit  35  discards the address of the SGSN  10  upon the mobile terminal  40  moving to an area of another SGSN  10 . The communication state determination unit  36  determines that the mobile terminal  40  is in communication in the case where the address of the GGSN  20  is stored in the communication state storage unit  35  and determines that the mobile terminal  40  is not in communication in the case where it is not stored. The address of the SGSN  10  stored in the communication state storage unit  35  is used to identify the SGSN  10  in the transmission of the charge remaining amount to the SGSN  10  from the stored remaining amount transmission unit  32  and the reception of the charge remaining amount by the updated remaining amount reception unit  33  from the SGSN  10 . 
     The operation of the communication system  1  in the case where the SGSN  10  calculates the communication packet volume will be described with reference to  FIG. 6 .  FIG. 6  is a flowchart illustrating the procedure of the charge remaining amount notification process in the case where the SGSN calculates the communication volume. First, the mobile terminal  40  requests a location registration from the SGSN  10  upon entering into a service area of the SGSN  10  (step S 201 ). The SGSN  10  that has received a location registration request transmits the address of the SGSN  10  from the communication state transmission unit  12  to the service control device  30  (step S 202 ). The service control device  30  receives the address of the SGSN  10  with the communication state reception unit  34  and stores it in the communication state storage unit  35  (step S 203 ). 
     Subsequently, communication of the mobile terminal  40  and the connection destination  60  is made possible by similar processes as in steps S 103  to S 105  described above (steps S 204  to S 206 ), and the address of the GGSN  20  is transmitted from the GGSN  20  to the service control device  30  (step S 207 ). The service control device  30  receives the address of the GGSN  20  with the communication state reception unit  34  and stores it in the communication state storage unit  35  (step S 208 ). 
     Next, the service control device  30  transmits the charge remaining amount stored in the remaining amount storage unit  31  from the stored remaining amount transmission unit  32  to the SGSN  10  (step S 209 ). A transmission destination in step S 209  is identified by the address of the SGSN  10  stored in the communication state storage unit  35 . The SGSN  10  receives the charge remaining amount with the stored remaining amount reception unit  14  and performs an update of the charge remaining amount with the remaining amount update unit  15  (step S 210 ). 
     When the user of the mobile terminal  40 , for example, inputs an inquiry for the charge remaining amount to the charge site  70 , the service control device  30  accepts the inquiry for the charge remaining amount with the inquiry acceptance unit  37  (step S 211 ). Next, the service control device  30  determines with the communication state determination unit  36  whether the mobile terminal  40  is in communication (step S 212 ). 
     When the communication state determination unit  36  determines that the mobile terminal  40  is in communication, the service control device  30  requests the updated charge remaining amount from the SGSN  10  (step S 213 ). A request destination in step S 213  is identified by the address of the SGSN  10  stored in the communication state storage unit  35 . The SGSN  10  that has received a request for the charge remaining amount transmits the charge remaining amount from the updated remaining amount transmission unit  16  to the service control device  30  (step S 214 ). The service control device  30  receives the charge remaining amount with the updated remaining amount reception unit  33  and outputs the received charge remaining amount from the remaining amount notification unit  38  to the charge site  70  (step S 215 ). Accordingly, the charge remaining amount is notified to, for example, the user of the mobile terminal  40 . 
     When the communication state determination unit  36  determines that the mobile terminal  40  is not in communication, the service control device  30  outputs the charge remaining amount stored in the remaining amount storage unit  31  from the remaining amount notification unit  38  to the charge site  70  (step S 215 ). 
     In the case where the SGSN  10  calculates the communication packet volume, load in a process of calculating the communication packet volume of the mobile terminal  40  is distributed to the SGSN  10  arranged for each communication area. 
     A preferred embodiment of the present invention has been described above. However, the present invention is not necessarily limited to the embodiment described above, and various modifications are possible without departing from the gist thereof. 
     The GGSN  20  transmits the address of the GGSN  20  as the information indicating the communication state of the mobile terminal  40 , and the service control device  30  stores the address of the GGSN  20  and determines whether the mobile terminal  40  is in communication on the basis of whether the address of the GGSN  20  is stored. However, the invention is not limited thereto. For example, the GGSN  20  may transmit information indicating the start and the termination of communication of the mobile terminal  40 . In this case, the service control device  30  stores flag data indicating the communication state of the mobile terminal  40 , causes the flag data to be in an on-state at the time of the start of communication of the mobile terminal  40 , causes the flag data to be in an off-state at the time of the termination of communication of the mobile terminal  40 , and determines whether the mobile terminal  40  is in communication on the basis of whether the flag data is in the on-state or in the off-state, for example. 
     The charge remaining amount of the mobile terminal  40  in communication is acquired by the GGSN  20  or the SGSN  10  and updated in the GGSN  20  or the SGSN  10 . However, the invention is not limited thereto. For example, the service control device  30  may acquire the communication packet volume calculated by the GGSN  20  or the SGSN  10  and update the charge remaining amount of the mobile terminal  40 . 
     The embodiment described above mainly uses a GPRS communication system, but the invention is not limited to such communication systems. It is appropriately applicable in communication systems in which packet data can be communicated, and it is also applicable in a novel communication system such as Long Term Evolution (LTE). In that regard, corresponding to the GGSN  20  is a Packet Data Network Gateway (P-GW), and corresponding to the SGSN  10  is a Mobility Management Entity (MIME) or a Serving Gateway (S-GW). Corresponding to the service control device  30  is a Home Subscriber System (HSS). Note that a Policy and Charging Rule Function (PCRF) may be used as the service control device  30 . 
     INDUSTRIAL APPLICABILITY 
     The present invention can be utilized in a communication system for a mobile terminal. 
     REFERENCE SIGNS LIST 
       1  . . . communication system,  10  . . . SGSN (communication control device),  20  . . . GGSN (communication control device),  30  . . . service control device,  33  . . . updated remaining amount reception unit,  35  . . . communication state storage unit,  36  . . . communication state determination unit,  37  . . . inquiry acceptance unit,  38  . . . remaining amount notification unit.